diff --git a/addons/project/controllers/portal.py b/addons/project/controllers/portal.py
index a6a5e1bbf7b..7737d1dc153 100644
--- a/addons/project/controllers/portal.py
+++ b/addons/project/controllers/portal.py
@@ -11,7 +11,7 @@ from odoo.http import request
 from odoo.addons.portal.controllers.portal import CustomerPortal, pager as portal_pager
 from odoo.tools import groupby as groupbyelem
 
-from odoo.osv.expression import OR
+from odoo.osv.expression import OR, AND
 
 from odoo.addons.web.controllers.main import HomeStaticTemplateHelpers
 
@@ -177,6 +177,38 @@ class ProjectCustomerPortal(CustomerPortal):
         values['project'] = project_sudo
         return request.render("project.portal_my_task", values)
 
+    @http.route('/my/projects/<int:project_id>/task/<int:task_id>/subtasks', type='http', auth='user', methods=['GET'], website=True)
+    def portal_my_project_subtasks(self, project_id, task_id, page=1, date_begin=None, date_end=None, sortby=None, filterby=None, search=None, search_in='content', groupby=None, **kw):
+        try:
+            project_sudo = self._document_check_access('project.project', project_id)
+            task_sudo = request.env['project.task'].search([('project_id', '=', project_id), ('id', '=', task_id)]).sudo()
+            task_domain = [('id', 'child_of', task_id), ('id', '!=', task_id)]
+            searchbar_filters = self._get_my_tasks_searchbar_filters([('id', '=', task_sudo.project_id.id)], task_domain)
+
+            if not filterby:
+                filterby = 'all'
+            domain = searchbar_filters.get(filterby, searchbar_filters.get('all'))['domain']
+
+            values = self._prepare_tasks_values(page, date_begin, date_end, sortby, search, search_in, groupby, url=f'/my/projects/{project_id}/task/{task_id}/subtasks', domain=AND([task_domain, domain]))
+            values['page_name'] = 'project_subtasks'
+
+            # pager
+            pager_vals = values['pager']
+            pager_vals['url_args'].update(filterby=filterby)
+            pager = portal_pager(**pager_vals)
+
+            values.update({
+                'project': project_sudo,
+                'task': task_sudo,
+                'grouped_tasks': values['grouped_tasks'](pager['offset']),
+                'pager': pager,
+                'searchbar_filters': OrderedDict(sorted(searchbar_filters.items())),
+                'filterby': filterby,
+            })
+            return request.render("project.portal_my_tasks", values)
+        except (AccessError, MissingError):
+            return request.not_found()
+
     # ------------------------------------------------------------
     # My Task
     # ------------------------------------------------------------
@@ -357,14 +389,13 @@ class ProjectCustomerPortal(CustomerPortal):
         })
         return values
 
-    @http.route(['/my/tasks', '/my/tasks/page/<int:page>'], type='http', auth="user", website=True)
-    def portal_my_tasks(self, page=1, date_begin=None, date_end=None, sortby=None, filterby=None, search=None, search_in='content', groupby=None, **kw):
+    def _get_my_tasks_searchbar_filters(self, project_domain=None, task_domain=None):
         searchbar_filters = {
             'all': {'label': _('All'), 'domain': []},
         }
 
         # extends filterby criteria with project the customer has access to
-        projects = request.env['project.project'].search([])
+        projects = request.env['project.project'].search(project_domain or [])
         for project in projects:
             searchbar_filters.update({
                 str(project.id): {'label': project.name, 'domain': [('project_id', '=', project.id)]}
@@ -372,7 +403,7 @@ class ProjectCustomerPortal(CustomerPortal):
 
         # extends filterby criteria with project (criteria name is the project id)
         # Note: portal users can't view projects they don't follow
-        project_groups = request.env['project.task'].read_group([('project_id', 'not in', projects.ids)],
+        project_groups = request.env['project.task'].read_group(AND([[('project_id', 'not in', projects.ids)], task_domain or []]),
                                                                 ['project_id'], ['project_id'])
         for group in project_groups:
             proj_id = group['project_id'][0] if group['project_id'] else False
@@ -380,6 +411,11 @@ class ProjectCustomerPortal(CustomerPortal):
             searchbar_filters.update({
                 str(proj_id): {'label': proj_name, 'domain': [('project_id', '=', proj_id)]}
             })
+        return searchbar_filters
+
+    @http.route(['/my/tasks', '/my/tasks/page/<int:page>'], type='http', auth="user", website=True)
+    def portal_my_tasks(self, page=1, date_begin=None, date_end=None, sortby=None, filterby=None, search=None, search_in='content', groupby=None, **kw):
+        searchbar_filters = self._get_my_tasks_searchbar_filters()
 
         if not filterby:
             filterby = 'all'
@@ -406,7 +442,7 @@ class ProjectCustomerPortal(CustomerPortal):
         raise MissingError(_('There is nothing to report.'))
 
     @http.route(['/my/tasks/<int:task_id>'], type='http', auth="public", website=True)
-    def portal_my_task(self, task_id, report_type=None, access_token=None, **kw):
+    def portal_my_task(self, task_id, report_type=None, access_token=None, project_sharing=False, **kw):
         try:
             task_sudo = self._document_check_access('project.task', task_id, access_token)
         except (AccessError, MissingError):
@@ -418,5 +454,9 @@ class ProjectCustomerPortal(CustomerPortal):
         # ensure attachment are accessible with access token inside template
         for attachment in task_sudo.attachment_ids:
             attachment.generate_access_token()
+        if project_sharing is True:
+            # Then the user arrives to the stat button shown in form view of project.task and the portal user can see only 1 task
+            # so the history should be reset.
+            request.session['my_tasks_history'] = task_sudo.ids
         values = self._task_get_page_view_values(task_sudo, access_token, **kw)
         return request.render("project.portal_my_task", values)
diff --git a/addons/project/models/project.py b/addons/project/models/project.py
index 3e2565c0a44..fd26fbea16b 100644
--- a/addons/project/models/project.py
+++ b/addons/project/models/project.py
@@ -2160,6 +2160,22 @@ class Task(models.Model):
         action['views'] = [[self.env.ref('project.project_sharing_project_task_view_form').id, 'form']]
         return action
 
+    def action_project_sharing_open_subtasks(self):
+        self.ensure_one()
+        subtasks = self.env['project.task'].search([('id', 'child_of', self.id), ('id', '!=', self.id)])
+        if subtasks.project_id == self.project_id:
+            action = self.env['ir.actions.act_window']._for_xml_id('project.project_sharing_project_task_action_sub_task')
+            if len(subtasks) == 1:
+                action['view_mode'] = 'form'
+                action['views'] = [(view_id, view_type) for view_id, view_type in action['views'] if view_type == 'form']
+                action['res_id'] = subtasks.id
+            return action
+        return {
+            'name': 'Portal Sub-tasks',
+            'type': 'ir.actions.act_url',
+            'url': f'/my/projects/{self.project_id.id}/task/{self.id}/subtasks' if len(subtasks) > 1 else subtasks.get_portal_url(query_string='project_sharing=1'),
+        }
+
     def action_dependent_tasks(self):
         self.ensure_one()
         action = {
diff --git a/addons/project/views/project_portal_templates.xml b/addons/project/views/project_portal_templates.xml
index f2fb8fb2edb..2e055e463d1 100644
--- a/addons/project/views/project_portal_templates.xml
+++ b/addons/project/views/project_portal_templates.xml
@@ -6,7 +6,7 @@
                 <a t-if="project" t-attf-href="/my/projects?{{ keep_query() }}">Projects</a>
                 <t t-else="">Projects</t>
             </li>
-            <li t-if="page_name == 'project_task' and project" class="breadcrumb-item active">
+            <li t-if="page_name in ['project_task', 'project_subtasks'] and project" class="breadcrumb-item active">
                 <a t-if="project" t-attf-href="/my/projects/{{ project.id }}?{{ keep_query() }}"><t t-esc="project.name"/></a>
             </li>
             <li t-elif="project" t-attf-class="breadcrumb-item #{'active ' if not project else ''} text-truncate col-8 col-lg-10">
@@ -16,9 +16,19 @@
                 <a t-if="task" t-attf-href="/my/tasks?{{ keep_query() }}">Tasks</a>
                 <t t-else="">Tasks</t>
             </li>
-            <li t-if="task" class="breadcrumb-item active text-truncate">
+            <li t-if="page_name == 'project_subtasks' and task and project" class="breadcrumb-item active">
+                <a t-attf-href="/my/projects/{{ project.id }}/task/{{ task.id }}?{{ keep_query() }}"><t t-esc="task.name"/></a>
+            </li>
+            <li t-elif="task" class="breadcrumb-item active text-truncate">
                 <span t-field="task.name"/>
             </li>
+            <li t-if="page_name == 'project_subtasks' or (task and subtask and project)" t-attf-class="breadcrumb-item text-truncate #{'active ' if not subtask else ''}">
+                <a t-if="subtask" t-attf-href="/my/tasks/{{ task.id }}/subtasks?{{ keep_query() }}">Sub-tasks</a>
+                <t t-else="">Sub-tasks</t>
+            </li>
+            <li t-if="subtask" class="breadcrumb-item active text-truncate">
+                <span t-field="subtask.name"/>
+            </li>
         </xpath>
     </template>
 
diff --git a/addons/project/views/project_sharing_views.xml b/addons/project/views/project_sharing_views.xml
index 7a0a6164622..f5e0ff3ef8a 100644
--- a/addons/project/views/project_sharing_views.xml
+++ b/addons/project/views/project_sharing_views.xml
@@ -161,6 +161,15 @@
                     <div class="oe_button_box" name="button_box">
                         <field name="display_parent_task_button" invisible="1"/>
                         <button name="action_project_sharing_view_parent_task" type="object" class="oe_stat_button" icon="fa-tasks" string="Parent Task" attrs="{'invisible': [('display_parent_task_button', '=', False)]}"/>
+                        <button name="action_project_sharing_open_subtasks" type="object" class="oe_stat_button" icon="fa-tasks"
+                            attrs="{'invisible' : ['|', '|', ('allow_subtasks', '=', False), ('id', '=', False), ('subtask_count', '=', 0)]}" context="{'default_user_ids': [(6, 0, [uid])]}">
+                            <div class="o_field_widget o_stat_info">
+                                <span class="o_stat_value">
+                                    <field name="subtask_count" widget="statinfo" nolabel="1"/>
+                                </span>
+                                <span class="o_stat_text">Sub-tasks</span>
+                            </div>
+                        </button>
                     </div>
                     <widget name="web_ribbon" title="Archived" bg_color="bg-danger" attrs="{'invisible': [('active', '=', True)]}"/>
                     <div class="oe_title pr-0">
@@ -305,4 +314,39 @@
         <field name="view_id" ref="project.project_sharing_project_task_view_form"/>
     </record>
 
+    <record id="project_sharing_project_task_action_sub_task" model="ir.actions.act_window">
+        <field name="name">Sub-tasks</field>
+        <field name="res_model">project.task</field>
+        <field name="view_mode">tree,kanban,form</field>
+        <field name="search_view_id" ref="project.project_sharing_project_task_view_search"/>
+        <field name="domain">[('id', 'child_of', active_id), ('id', '!=', active_id)]</field>
+        <field name="context">{'default_parent_id': active_id}</field>
+        <field name="help" type="html">
+            <p class="o_view_nocontent_smiling_face">
+                No tasks found. Let's create one!
+            </p><p>
+                To get things done, use activities and status on tasks.<br/>
+                Chat in real time or by email to collaborate efficiently.
+            </p>
+        </field>
+    </record>
+
+    <record id="project_sharing_subtasks_tree_action_view" model="ir.actions.act_window.view">
+        <field name="view_mode">tree</field>
+        <field name="act_window_id" ref="project.project_sharing_project_task_action_sub_task"/>
+        <field name="view_id" ref="project.project_sharing_project_task_view_tree"/>
+    </record>
+
+    <record id="project_sharing_subtasks_kanban_action_view" model="ir.actions.act_window.view">
+        <field name="view_mode">kanban</field>
+        <field name="act_window_id" ref="project.project_sharing_project_task_action_sub_task"/>
+        <field name="view_id" ref="project.project_sharing_project_task_view_kanban"/>
+    </record>
+
+    <record id="project_sharing_subtasks_form_action_view" model="ir.actions.act_window.view">
+        <field name="view_mode">form</field>
+        <field name="act_window_id" ref="project.project_sharing_project_task_action_sub_task"/>
+        <field name="view_id" ref="project.project_sharing_project_task_view_form"/>
+    </record>
+
 </odoo>