diff --git a/src/components/AppSidebar/DateTimePickerItem.vue b/src/components/AppSidebar/DateTimePickerItem.vue
index 54066724e..e5e7c9f8f 100644
--- a/src/components/AppSidebar/DateTimePickerItem.vue
+++ b/src/components/AppSidebar/DateTimePickerItem.vue
@@ -115,6 +115,13 @@ export default {
 			type: Boolean,
 			default: false,
 		},
+		/**
+		 * Whether the date can be considered 'overdue'
+		 */
+		checkOverdue: {
+			type: Boolean,
+			default: true,
+		}
 	},
 	data() {
 		return {
@@ -139,7 +146,7 @@ export default {
 			return this.date.isValid()
 		},
 		isOverdue() {
-			return overdue(this.date)
+			return this.checkOverdue && overdue(this.date)
 		},
 	},
 	methods: {
diff --git a/src/models/task.js b/src/models/task.js
index bc5a20da9..f0945ff1c 100644
--- a/src/models/task.js
+++ b/src/models/task.js
@@ -306,12 +306,14 @@ export default class Task {
 		}
 	}
 
-	setCompleted(completed) {
+	setCompleted(completed, completedDate = null) {
 		if (completed) {
-			const now = ICAL.Time.fromJSDate(new Date(), true)
-			this.vtodo.updatePropertyWithValue('completed', now)
-			this._completedDate = now
-			this._completedDateMoment = moment(now, 'YYYYMMDDTHHmmssZ')
+			if (completedDate === null) {
+				completedDate = ICAL.Time.fromJSDate(new Date(), true)
+			}
+			this.vtodo.updatePropertyWithValue('completed', completedDate)
+			this._completedDate = completedDate
+			this._completedDateMoment = moment(completedDate, 'YYYYMMDDTHHmmssZ')
 		} else {
 			this.vtodo.removeProperty('completed')
 			this._completedDate = null
@@ -325,6 +327,20 @@ export default class Task {
 		return this._completedDate
 	}
 
+	set completedDate(completedDate) {
+		if (completedDate) {
+			this.setCompleted(true, completedDate)
+			this.setComplete(100)
+			this.setStatus('COMPLETED')
+		} else {
+			this.setCompleted(false)
+			if (this.complete === 100) {
+				this.setComplete(99)
+				this.setStatus('IN-PROCESS')
+			}
+		}
+	}
+
 	get completedDateMoment() {
 		return this._completedDateMoment.clone()
 	}
diff --git a/src/store/tasks.js b/src/store/tasks.js
index 15603a632..0b92596b8 100644
--- a/src/store/tasks.js
+++ b/src/store/tasks.js
@@ -605,6 +605,29 @@ const mutations = {
 		}
 	},
 
+	/**
+	 * Sets the completed date of a task
+	 *
+	 * @param {object} state The store data
+	 * @param {object} data Destructuring object
+	 * @param {Task} data.task The task
+	 * @param {moment|null} data.completedDate The completed date moment
+	 */
+	setCompletedDate(state, { task, completedDate }) {
+		if (completedDate !== null) {
+			// Check that the completed date is in the past.
+			const now = moment(ICAL.Time.fromJSDate(new Date(), true), 'YYYYMMDDTHHmmssZ')
+			if (completedDate.isAfter(now)) {
+				showError(t('tasks', 'Completion date must be in the past.'))
+				return
+			}
+			// Convert completed date to ICALTime first
+			completedDate = momentToICALTime(completedDate, false)
+		}
+		// Set the completed date
+		task.completedDate = completedDate
+	},
+
 	/**
 	 * Toggles if the start and due dates of a task are all day
 	 *
@@ -1318,6 +1341,17 @@ const actions = {
 		context.dispatch('updateTask', task)
 	},
 
+	/**
+	 * Sets the completed date of a task
+	 *
+	 * @param {object} context The store context
+	 * @param {Task} task The task to update
+	 */
+	async setCompletedDate(context, { task, completedDate }) {
+		context.commit('setCompletedDate', { task, completedDate })
+		context.dispatch('updateTask', task)
+	},
+
 	/**
 	 * Sets the start or due date to the given day
 	 *
diff --git a/src/views/AppSidebar.vue b/src/views/AppSidebar.vue
index 5fe9bc0b7..fb24cc336 100644
--- a/src/views/AppSidebar.vue
+++ b/src/views/AppSidebar.vue
@@ -166,6 +166,18 @@ License along with this library. If not, see <http://www.gnu.org/licenses/>.
 					:placeholder="t('tasks', 'Select a status')"
 					icon="IconPulse"
 					@change-value="changeStatus" />
+				<DateTimePickerItem v-show="task.completed"
+					:date="task.completedDateMoment"
+					:value="newCompletedDate"
+					:property-string="completedString"
+					:read-only="readOnly"
+					:task="task"
+					:check-overdue=false
+					@set-value="changeCompletedDate">
+					<template #icon>
+						<CalendarCheck :size="20" />
+					</template>
+				</DateTimePickerItem>
 				<SliderItem v-show="!readOnly || task.priority"
 					:value="task.priority"
 					:property-string="priorityString"
@@ -289,6 +301,7 @@ import NcLoadingIcon from '@nextcloud/vue/dist/Components/NcLoadingIcon.js'
 import { generateUrl } from '@nextcloud/router'
 
 import Calendar from 'vue-material-design-icons/Calendar.vue'
+import CalendarCheck from 'vue-material-design-icons/CalendarCheck.vue'
 import CalendarEnd from 'vue-material-design-icons/CalendarEnd.vue'
 import CalendarStart from 'vue-material-design-icons/CalendarStart.vue'
 import Delete from 'vue-material-design-icons/Delete.vue'
@@ -319,6 +332,7 @@ export default {
 		Calendar,
 		CalendarEnd,
 		CalendarStart,
+		CalendarCheck,
 		Delete,
 		Download,
 		InformationOutline,
@@ -549,6 +563,18 @@ export default {
 			}
 			return reference.toDate()
 		},
+		/**
+		 * Initializes the completed date of a task
+		 *
+		 * @return {Date|null} The completed date moment
+		 */
+		 newCompletedDate() {
+			const completedDate = this.task.completedDateMoment
+			if (completedDate.isValid()) {
+				return completedDate.toDate()
+			}
+			return null
+		},
 		taskStatusLabel() {
 			return this.loading ? t('tasks', 'Loading task from server.') : t('tasks', 'Task not found!')
 		},
@@ -709,6 +735,7 @@ export default {
 			'addTag',
 			'setDue',
 			'setStart',
+			'setCompletedDate',
 			'toggleAllDay',
 			'moveTask',
 			'setClassification',
@@ -817,6 +844,23 @@ export default {
 			this.setDue({ task, due, allDay: this.allDay })
 		},
 
+		/**
+		 * Sets the completed date to the given Date or to null
+		 *
+		 * @param {object} context The data object
+		 * @param {Task} context.task The task for which to set the date
+		 * @param {Date|null} context.value The new completed date
+		 */
+		 changeCompletedDate({ task, value: completedDate }) {
+			if (completedDate) {
+				completedDate = moment(completedDate)
+			}
+			if (this.task.completedDateMoment.isSame(completedDate)) {
+				return
+			}
+			this.setCompletedDate({ task, completedDate })
+		},
+
 		changeClass(classification) {
 			this.setClassification({ task: this.task, classification: classification.type })
 		},
diff --git a/tests/javascript/unit/views/AppSidebar.spec.js b/tests/javascript/unit/views/AppSidebar.spec.js
index 484121f05..2217bbbe1 100644
--- a/tests/javascript/unit/views/AppSidebar.spec.js
+++ b/tests/javascript/unit/views/AppSidebar.spec.js
@@ -55,4 +55,39 @@ describe('AppSidebar.vue', () => {
 		actual = wrapper.vm.newDueDate
 		expect(actual.getTime()).toBe(newDueDate.getTime())
 	})
+
+	it('Task completed date is set correctly', () => {
+		const wrapper = shallowMount(AppSidebar, {
+			global: {
+				plugins: [store, router],
+			},
+		})
+
+		let actual = wrapper.vm.newCompletedDate
+		expect(actual).toBe(null)
+
+		const newCompletedDate = new Date('2019-01-01T12:00:00')
+		wrapper.vm.changeCompletedDate({ task: wrapper.vm.task, value: newCompletedDate })
+
+		actual = wrapper.vm.newCompletedDate
+		expect(actual.getTime()).toBe(newCompletedDate.getTime())
+	})
+
+	it('Setting completed date to future is ignored', () => {
+		const wrapper = shallowMount(AppSidebar, {
+			global: {
+				plugins: [store, router],
+			},
+		})
+
+		let actual = wrapper.vm.newCompletedDate
+		const expected = new Date('2019-01-01T12:00:00')
+		expect(actual.getTime()).toBe(expected.getTime())
+
+		const newCompletedDate = new Date('2020-01-01T12:00:01')
+		wrapper.vm.changeCompletedDate({ task: wrapper.vm.task, value: newCompletedDate })
+
+		actual = wrapper.vm.newCompletedDate
+		expect(actual.getTime()).toBe(expected.getTime())
+	})
 })