A native of Toronto, Ontario, Trevor was selected 43rd overall in the 2002 NHL Entry Draft by the Dallas Stars. He made his NHL debut with the Stars in the 2003–04 season and established himself as a regular in the 2005–06 season, playing in a career-high 81 games. Trevor was later traded to the Chicago Blackhawks and then to the Pittsburgh Penguins where he played an integral role in the Penguins back-to-back Stanley Cup Championships in 2015-16 and 2016-17. Prior to the 2017-18 season Trevor signed as a free agent with the Detroit Red Wings.
Internationally, Daley was a member of the Canadian team at the 2006 World Hockey Championships.