The veteran goalkeeper, 40, left Hammer as a free agent at the end of last season, spending seven years with the club and making 216 appearances.
Fabianski’s arrival comes after Wes Foderingham leaves to join Alice Limassol on the Cypriot side.
“I’m really, really, really, really, really, really, really, really, really, really, really, really, happy because this club clearly means a lot to me and the people at this club,” Fabianski said.
“I looked again and found it wonderful and beautiful.
“I’ve always been there, and I’m certainly going to be a player who always surpasses my personal goals.
“Then people might think that it’s a good person to be around me, and I think that it’s a good person to be on the team in terms of what I bring.
“I’m here to support you and keep the standards high. I have a lot of experience as well, so I think it’s useful.
“It’s true, I’ll continue to work the way I always do it. I hope that it’s always on a good level, but at the same time I understand that my role is completely different.”
Coach Graham Potter welcomed the Polish shot stopper as “a top goalkeeper and top professional.”
“I’m so happy that Lukas is back in the group,” Potter said.
“Regardless of what he was here before, the main factor is that he is still the top goalkeeper, top expert and the perfect choice for the role we need to fill.
“It’s a signature that makes perfect sense to everyone. Lukasz knows the club very well and is very respected and popular among everyone here.
“His personality and personality are a great example, especially for young players. He’s someone who really cares about West Ham United and wants to help us as much as he can.
