The former Southampton stopper left Coventry City at the end of the season and has now joined Alan Archibald’s side ahead of the new Premiership campaign.
Seabourne follows Ryan Stevenson and Abdul Osman in making the switch to Firhill this summer and could make his debut when the Jags host Ross County in their top-flight opener on Wednesday night.
Thistle finished tenth on their return to the Premiership last time out and midfielder Stuart Bannigan admits Archibald’s squad are in good spirits ahead of the big kick-off.
He said: “The boys are confident going into the season. We’ve got a couple of really good signings who have come in to gel with the players who have been here for quite a few years now.
“We feel good going into it and hopefully we can do well.
“We’ll go into the games with the same aim as last season, to try and play good football like we always try and do.
“We will be trying to maybe finish a wee bit higher up the league though. It’s going to be tough, we know that, there are a few new teams in the league who will be excited to be back in the Premiership so we have to be on our guard.”
Thistle rounded off their pre-season schedule with an impressive performance in a 3-0 win over Sunderland at Firhill last week.
And Bannigan was delighted to get some much-needed game time under his belt after an injury-hit summer so far.
“Everything is feeling alright so I’m delighted,” he told ptfc.co.uk
“I’ve trained for the last week or so now so I just needed to get a wee game to put it to the test and I’ve come through ok.
“It’s just a case of stepping training up before the competitive action starts so I can be ready to go.”