Williams, 30, is a 10-year NHL veteran who played in 27 games with the Dallas Stars last season, scoring five points. The 5-foot-11, 192-pound right winger has also played for the Detroit Red Wings, Chicago Blackhawks, Columbus Blue Jackets and Atlanta Thrashers.
Williams was a member of the Red Wings' 2001-02 Stanley Cup championship squad, appearing in nine postseason games that spring.
He had his best season in 2005-06 with Detroit, posting career highs in games played (80), goals (21), assists (37) and points (58).
Williams is a native of London, Ontario, and has appeared in 447 regular-season NHL games. He has 93 career goals and 225 points.
The Penguins also signed defenseman Scott Harrington, their 6-foot, 200-pound second-round pick, to a three-year contract. Harrington, 18, was chosen with the 54th overall selection in June. He attended the Penguins' annual prospect development camp earlier this month.
"Scott will continue his development in junior hockey this season with the London Knights of the Ontario Hockey League, and we look forward to watching his progress," assistant to the general manager Tom Fitzgerald said. "The three-year term will begin when he makes the transition to pro hockey, but we are pleased to get him signed at this point and have him as a part of the Penguins organization and part of our future."
Harrington is a native of Kingston, Ontario, who has played two seasons already with London, totaling 36 points.