The defender made his Jags bow in the 1-1 draw with Kilmarnock on Saturday just hours after agreeing a short-term deal from St Mirren and linking up with his former team-mate.
Thistle face St Johnstone tonight aiming to move out of the relegation play-off zone and Mair insists Archibald has the quality to lead his troops in battle.
He said: "We were team-mates at Dundee United and I did the coaching A Licence with him in the summer as well, so we've been speaking.
"There were sniffs about me coming here in the summer but nothing materialised so I decided to stick at St Mirren and give it a try.
"I got back in the team, played well, and still didn't keep my place in the team. That made me realise it was time to go.
"When the chance came up again to come here I thought 'definitely, I'm off'.
"I never turned it down this time and I'm now just looking forward to the remaining games of the season.
"You knew Archie was a leader on the park and off it as well. He was a good guy and everyone liked him.
"He's a likeable guy - after the game on Saturday was actually the first time I had seen him angry.
"He's a nice guy but he was obviously upset that we had lost two points. You can see he's become a different character as a manager, you've got to.
"I've obviously only been here a short time but you can see that he's changed.
"He used to be a bit of a joker in the dressing room and now he has to take himself away from that, be a serious man. It seems like he's adapting to it well."