The 21-year-old midfielder arrives from Championship side Dundee United having started his career at Queen’s Park.
Speaking about his first signing of the summer, Jags boss Alan Archibald told the club’s official website: “Blair is a player who we have been monitoring for a while and I am delighted to see him sign for us today.
“He is an exciting young player who will add a really strong and threat to our wide areas.
“I think Blair will bring a creative force to our team and I hope he can continue the excellent form he showed at the end of last season.
“We have a really good group of lads and I definitely think Spittal compliments what is already here.”