Pat, who helped Ayr lift the SHE Premier One title in 2009, said: "I've already experienced professional rugby with the Warriors so I'm really excited that Sean has given me this opportunity to join the squad fulltime.
"I've been in the National Academy for the last two years and it's a great feeling to finally realise a lifelong ambition of becoming a Glasgow player.
"Having won Premier One with Ayr this season, this caps off a fantastic season for me personally."
Glasgow coach Sean Lineen said: "He has been on the fringes for a couple of years now. He has physically developed very well and he is ready for the professional ranks now. With the right attitude he will push both Dougie Hall and Fergus Thomson all the way."
Scottish Rugby's National Academy Manager, Stephen Gemmell, added: "Once more, we can see that the Academy structure is producing players of the calibre that our professional teams are looking for.
"Both these players have performed to a very high standard and are worthy of the professional contracts handed to them today. I'm certain that they'll continue to flourish as they graduate into the professional ranks."