He played in Major League Baseball (MLB) for the Seattle Mariners, San Francisco Giants, Oakland Athletics, Houston Astros, and Texas Rangers.

Blackley also played in the KBO League for the Kia Tigers and in Nippon Professional Baseball (NPB) for the Tohoku Rakuten Golden Eagles.

The Mariners, after trading Freddy García to the Chicago White Sox, needed another starter and purchased Blackley's contract on 1 July 2004.

He made his major league debut on that same day against the Texas Rangers and beat them, allowing 4 runs on 6 hits in 5⅔ innings.

He became just the sixth Mariner pitcher in the team's history to start and win his major league debut.

After spending a month with the major league club going only 1–3 with a 10.04 ERA in 6 starts, Blackley was optioned back to Triple-A Tacoma on 1 August 2004.

He had an 8–6 record with a 3.83 ERA in 19 games (18 starts) with Tacoma in 2004 before ending the season on the disabled list with left shoulder tendinitis.

In March 2006, Blackley was slated to play in the World Baseball Classic with team Australia but was scratched to continue rehabbing his shoulder.

On 1 April 2007, after spring training, he was traded to the San Francisco Giants for outfielder Jason Ellison and was immediately optioned to Triple-A Fresno, pitching the entire season in the minor leagues with the Grizzlies.

After being outrighted off the San Francisco roster on 6 December 2007, Blackley was selected by the Philadelphia Phillies in the major league portion of the Rule 5 draft.

On 4 April 2013, the Oakland Athletics traded Blackley to the Houston Astros for outfielder Jake Goebbert.

Travis made the 35-man roster of the Melbourne Aces for the inaugural Australian Baseball League season in 2010.

Blackley was first selected for Australia in the 2006 World Baseball Classic, but did not play due to an ongoing shoulder injury (as cited above).

He again pitched for Australia in the 2009 World Baseball Classic, earning a no-decision against Cuba and a 1.59 ERA for the tournament.

)[citation needed] His younger brother, Adam Blackley, formerly played in the Boston Red Sox farm system[10] as well as for the Melbourne Aces in the ABL and the L&D Amsterdam in the Dutch league Honkbal Hoofdklasse.