Sabres general manager Darcy Regier announced the trade Monday.
Roy is entering the final year of his contract after underperforming last season for Buffalo. Following season-ending surgery to repair a torn quadriceps tendon in 2010-2011, Roy had 17 goals and 27 assists in 80 games last season. He scored at least 25 goals from 2007-2010 before he was hurt. Roy has 161 goals and 266 assists in eight NHL seasons, all with Buffalo.
Ott had 11 goals and 28 assists in 74 games with the Stars last season. The 25th overall pick in the 2000 entry draft, Ott has 85 goals and 135 assists in 566 career games and the Sabres are hoping he can address criticism that the Sabres lack toughness.
Pardy spent his first three seasons with Calgary before joining the Stars in 2011-12, recording four goals, 25 assists and 157 penalty minutes in 183 NHL games.