The 38-year-old forward, who would have become an unrestricted free agent Wednesday, signed for $2 million, accepting a big pay cut to stay with a championship team after making $4.5 million last season with the Islanders and Penguins.
"There's a lot of good teams I could have played for but this obviously was the best fit," Guerin told ESPN.com's Pierre LeBrun late Monday.
Guerin, who will turn 39 in November, said he has not contemplated retirement.
"Maybe I should," Guerin said with a laugh, "but it really never crossed my mind. I knew I wanted to come back. My family and I have really enjoyed this."
Pittsburgh also signed Craig Adams, a fourth-line forward, to a $1.1 million, two-year contract. Adams made $600,000 last season. He will make $550,000 during each season of his new deal.
A 17-year NHL veteran, Guerin had seven goals and 15 points in the postseason after being acquired from the Islanders at the trading deadline in March, with all of his goals coming in the first three rounds. He has 408 goals and 811 points in 1,185 regular-season games with New Jersey, where he also won a Stanley Cup, Edmonton, Boston, Dallas, St. Louis and San Jose before joining the Islanders and then the Penguins.
"We are excited to agree to terms with Billy on this one-year deal," Penguins general manager Ray Shero said. "He made a tremendous impact on this team with his scoring ability, physical play and outstanding leadership and was a key factor in our drive to the Cup.
"I know our players, coaches and fans will be happy to have him back in Pittsburgh."
Guerin, obtained from the Islanders for a third-round draft pick, scored five goals and had seven assists in 17 regular-season games with the Penguins.
On being to continue playing alongside superstar center Sidney Crosby, Guerin told LeBrun, "I'd be lying if I didn't say that was one of the big reasons I wanted to stay. It's so much fun to play with him."
Adams had three goals and two assists in 24 playoff games for the Stanley Cup champs. He had two goals and four assists in 36 games with Chicago and one assist in nine regular-season games after being claimed off waivers by Pittsburgh on March 4.
Pierre LeBrun covers the NHL for ESPN.com. Information from The Associated Press was used in this report.