Roberts was acquired along with Ryan Malone from Pittsburgh on Saturday in exchange for a conditional draft pick in 2009. The Lightning and the unrestricted free agent agreed to a seven-year,
$31.5 million contract Sunday, ESPN.com confirmed on Monday.
Tampa Bay also acquired the rights to forward Brian Rolston, another player who could become an unrestricted free agent Tuesday, from Minnesota on Sunday and were trying to work out a contract with him.
Roberts, a three-time NHL All-Star, had three goals and 15 points with 40 penalty minutes in 38 games last season. He has played in 1,194 career games with Calgary, Carolina, Toronto, Florida and Pittsburgh, recording 434 career goals and 903 points.
Tampa Bay acquired the rights to Prospal on June 18 in return for two draft picks. He played in 62 games with the Lightning last season, picking up 29 goals and 57 points before being traded to Philadelphia on Feb. 25.
Also, the Lightning obtained minor league defenseman Janne Niskala from the Flyers for a sixth-round draft pick in 2009.
Information from The Associated Press was used in this report.