The singer appeared outside department store Frasers in Buchanan Street to mark the unveiling of his men's clothing label, Farrell.
Fans screamed and chanted 'Robbie' as he appeared for the photocall.
At the front of the crowd was Charmaine Stewart, 18, of Johnstone, Renfrewshire, who has a Robbie tattoo.
She said: "It's great he has come to Glasgow. I love everything about him."
Rosanna Burns, 26, from Yoker, Glasgow, took a break from working at Euro Hostel to catch a glimpse of her idol. She said: "I love him and his music."
Friend Karen Skillen, 48, added: "I like him because he is a cheeky chappie with a bit of charisma."
Robbie, 38, who is set to become a dad any day when wife Anya Field gives birth, named the clothing collection after his late grandad, Jack Farrell, and worked with his head of design, former Burberry designer Ben Dickens, on the range.
And he revealed as well as his grandad, his style icon is Scottish star Sean Connery, whose most famous role is as 007.
Robbie, who is about to release a new single called Candy, said: "The buck stops and starts with James Bond."
And he said he would like to see another Scot, Andy Murray, wearing his clothes, which includes scarves costing £25, coats from about £300 and shirts for £85.
Robbie said: "Andy Murray would be fantastic. But right now I just want to see anybody in it."
The singer also revealed he is a fan of another Scottish fashion icon - kilts.
He said: "I love wearing kilts. I've got loads. I've just been past a shop where they had a kilt and sporran and a Scotland football top, and I thought 'That would be a good look for a show here'."
Robbie said he was looking for something else to do alongside singing.
He said: "I wanted to do something else. This is what I will fall back on. It's fun.
"In 2006 I finished a massive world tour. I played to three million people and got to the point where it was, ' What do you do next?' Four million? It's as big as it's going to get.
"It was put to me by my management that maybe I would like to put a clothing line together. And I thought 'I've worn clothes all my life. I must know how to do this.'
"My first version of a man on this planet was my grandad. He was from an era where, even if you were working class, you'd have a tailor, and you wore a three piece suit.
"I thought, 'What would grandad Jack want to wear?"
When asked if he would model his own clothes, he said: "Definitely, but I can't separate me from chocolate. I gave up smoking and put on two stones. Basically yes – if I can keep my feet out of the pantry."