Mulgrew celebrated the Player of the Year trophy, while teammate Jame Forrest picked up Young Player of the Year.
The Celtic team were denied a hat-trick of wins though when Ross County boss Derek Adams scooped the Manager of the Year award ahead of Parkhead boss Neil Lennon and Motherwell’s Stuart McCall.
Mulgrew and Forrest followed up their football writers’ Player and Young Player of the Year successes with a second double triumph in four days.
Forrest, who has had an explosive impact on Celtic’s title-winning season, said: “I am delighted to get the award because there were some top young players nominated.
“I owe everything to the manager and the coaching staff who have been a real help to me since I got into the first-team squad.”
Hoops boss Lennon was tipped to follow up his SFWA award but Adams pipped him and McCall to the manager’s trophy.
Adams led his team to the First Division title, losing just one game along the way. He said: “This has been a truly remarkable season and it’s an honour to be recognised in this way.”
Farid El Aligui, top scorer in the First Division, capped a sensational campaign at Falkirk by landing the First Division Player of the Year.
The sought-after striker said: “Being given this award is recognition of the way the manager (Steven Pressley) likes us to play.”
Cowdenbeath’s champions were recognised when Jon Robertson was voted Second Division Player of the Year.
The midfielder, who will play for St Mirren in the SPL next term, said: “People have been saying to me that it’s been a dream season and this just tops it all off.”
Third Division Player of the Year was won by Steven May, who helped Alloa to the title after being signed on loan from St Johnstone by boss Paul Hartley.
Goal of the season was won by Aberdeen’s Rory Fallon for his spectacular volley in the Scottish Cup semi-final defeat to Hibs at Hampden last month.
The New Zealander said: “It’s been a disappointing season for the club but I’m delighted to win this from a personal point of view.”
Former Rangers captain Ally Dawson won a Special Merit Award for his work with Scotland’s homeless football team.