Former Dundee United and Aberdeen midfielder Kerr has spent the past month training with the Firhill side and becomes boss Alan Archibald's third close-season signing after the capture of goalkeeper Paul Gallacher and frontman John Baird.
Balatoni, meanwhile, had another year to run on his contract but has agreed a one-year extension that will see him remain with the Maryhill outfit until the summer of 2015.
Kerr started his career with Falkirk and, as well as spells at Tannadice and Pittodrie, the former Scotland B cap has enjoyed stints at Dunfermline and Dundee.
The 31-year-old featured as a trialist in last night's 0-0 draw with Livingston and told the club's official website: "I've been here for nearly four weeks now so it will be good to get playing as an actual Partick Thistle player. I can now play at 100 per cent because you do tend to hold back a little.
"I do have that experience and hopefully I can start the season well and we can do well together. That's the way it goes - if I'm not playing well then I won't be in the team and I'll not be able to bring my experience to the team."
Meanwhile, Balatoni said he was delighted to sign on again with Thistle after helping the side win promotion and the Irn-Bru First Division championship last season.
"I've always been happy here and I'm happy to get it all sorted," the 22-year-old centre-back said. "Partick Thistle are a huge club with a good fan base and it's a club that deserves to be in the SPL. Over the years a squad was built good enough to get to the SPL and hopefully that same squad will be good enough to stay in the SPL.
"Staying in the league is going to be even harder than getting there. It's going to be hard but everyone is looking forward to it and everyone wants to prove themselves. The boys can't wait to get going and it is now just a matter of weeks everyone is looking forward to it."