Ruff made his firsts arms as a pro with the Peoria Rivermen, affiliate of the Blues, of the International Hockey League in the 1991 IHL playoffs. In 1991-92, Jason joined the Rivermen full-time. He would collect a good 72 points in 67 games in his rookie season. He split the next season between the Rivermen, the Atlanta Knights, the St. Louis Blues and the Tampa Bay Lightning. Over the course of that season and the next one, he would play 14 NHL games, scoring thrice and adding as many assists. That, however, would be all the NHL action Ruff would see in his career. He spent the next five seasons in the IHL with the Knights, the Quebec Rafales, the Cleveland Lumberjacks and the Houston Aeros before crossing the Atlantic in 1999 to join the Frankfurt Lions of the Deutsch Eishockey Liga.
In 2001, Ruff joined the Belfast Giants of the then British Super League. Except for a year with ERC Ingolstadt in 2002-03 and one with the Kansas City Outlaws of the United Hockey League in 2004-05, Ruff would play until his retirement in 2007 with the Giants, where he earned several distinctions, notably that of the player with the most points for 2003-04 with 86 (including 35 goals); this earned him the British Ice Hockey Writer's Association Player of the year title for that season, as well as a nomination to the league's all-star team.