Bialkowski, 24, joins after his contract at Saints expired this summer.
He made over 40 appearances since moving to St Mary's in 2006 and has represented Poland at Under-20 level.
"I'm really excited to be here, to join such a big club as Notts County, and hopefully next year we will win promotion," he told the club's official website.
"I came here because I want to play football and I will do my best to prove that I can be a top keeper. I have not given up on the national team, I still want to play for Poland."
Bialkowski joins as first-choice keeper after leaving Southampton in search of regular football.