The former Cappielow midfielder rejoins the club from the Scottish Premiership outfit, where he had been operating in a combined role as head of academy professional programmes and first-team coach.
His first match in charge of the Scottish Championship side will be the home fixture against Queen of the South on Boxing Day.
Morton director Graham Barr said: “It is great to be able to welcome Dougie Imrie to the club as our new first team manager.
“Following applications closing last week, a shortlist was produced by the board and candidates invited to interviews. Dougie was the standout candidate during the recruitment process, and his vision, ambition and enthusiasm for the club was clear to see.
“What was also clear to us in the interview process is that Dougie is both committed and determined to bring success to Morton, both in the short and long term.”
Imrie spent the 2013-14 season at Morton and scored a famous penalty kick winner against Celtic at Parkhead in the League Cup third round.
His playing career also included spells at Clyde, Inverness, St Mirren and Hamilton (twice).
"As a club, it’s never easy losing important members of staff but at the same time, it’s also pleasing to see staff who have become good friends go on and have opportunities that are progressive in their careers. Dougie goes with all our thanks and best wishes going forward.”