Having made the inaugural Play-Offs 13 months ago, the Warriors finished 11th in the Magners League standings this time around.
And with a host of star names set to travel to the World Cup with Scotland this autumn, the promising back rower's arrival at Firhill will be a big boost to Lineen and co.
"We're excited about adding Rory to the mix because he has a lot to offer and he is determined to hit the ground running," said Lineen.
"He's a big, ball-carrying back-rower and I'm delighted to have another talented player to add to our options in that area.
"The competition for places among the loosies is already pretty fierce, but across the board there is the opportunity for players to put their hand up and demand selection through the work they do in training.
"We've got three back-rowers in the wider Scotland squad for the Rugby World Cup, so it's good to be adding to our strength in depth.
"In terms of the deal itself, we had a similar situation last season with Tom Ryder, who initially came on loan, did really well and ended up signing for the club. Rory's deal is for six months - I look forward to seeing him contribute positively in that period and we'll then assess our options."
Pitman, who played three successive seasons of Under 20 rugby for Wales up until 2010 and has also spent a summer with Taranaki in New Zealand, is equally enthusiastic about the move.
"I'm delighted to be coming to Glasgow and can't wait to meet the rest of the squad in a couple of weeks' time," added Bridgend-born Pitman ahead of the start of the Warriors' pre-season training this coming Monday.
"The coaches have been very positive about what they think I can bring, and I was excited by what I saw when I came for a look around the training facilities at Scotstoun and heard Sean's passion for the club.
"My task is to work extremely hard and prove I'm worth a place in the team."
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