You can do this by checking `On Control Resolved Users Changed` event for the Client People picker. Please find more info [here][1] for Client People Picker Events. You can try following script block to check if user is already entered in people picker. this.SPClientPeoplePicker.SPClientPeoplePickerDict.peoplePickerDiv_TopSpan.OnUserResolvedClientScript = function (peoplePickerId, selectedUsersInfo) { console.log('inside OnUserResolvedClientScript'); var users = selectedUsersInfo; for(var i = 0; i < users.length - 1; i++){ if(users[users.length - 1].Key == users[i].Key){ alert("User already exists"); } } }; [1]: http://ranaictiu-technicalblog.blogspot.in/2014/11/sharepoint-2013-client-side-people.html