He has previously played in Major League Baseball (MLB) for the San Diego Padres, Cincinnati Reds, Philadelphia Phillies, New York Mets, Seattle Mariners, and Texas Rangers.

He attended Stony Brook University, where he led the Seawolves to a Cinderella appearance in the 2012 College World Series after upsetting the LSU Tigers.

Jankowski signed with the Rangers in 2023 and led the team in stolen bases en route to the franchise's first-ever World Series championship.

Following a season-ending injury to Adolis García in the World Series, Jankowski started in his place and had a multi-hit, multi-RBI showing in the Rangers' Game 4 win.

[2] Following his high school graduation in 2009, Jankowski committed to play college baseball at Stony Brook University on a partial athletic scholarship.

[2] Jankowski's slender frame, standing at 6 feet 2 inches (1.88 m) and 165 pounds (75 kg), made him a more appealing candidate for college baseball than football, and Stony Brook was the only NCAA Division I university to offer him a scholarship.

[9] Defensively, his performance in center field against North Carolina State helped take Stony Brook to its first ever NCAA tournament win.

He scored four hits in Stony Brook's 7–2 victory over Louisiana State to take the Baton Rouge Super Regional and reach the CWS.

[20] Jankowski, taken in the first round, was the highest MLB draft pick for the America East Conference since Carlos Peña, who attended Northeastern, was selected 10th overall in 1998.

[26] In the second game of the Midewst League championship series against the Wisconsin Timber Rattlers, Jankowski was hit by a pitch in his first at-bat, fracturing his rib.

Through mid-August, Jankowski led all professional baseball players in the United States with 71 stolen bases for the season; internationally, only Freddy Guzmán, who was playing at the time for the Delfines del Carmen of the Mexican League, had more.

[34] After a strong start to the season, hitting .254 in his first 67 at bats, Jankowski fractured his wrist by running headlong into the outfield fence while in pursuit of a fly ball.

[35] He underwent surgery for the injury, which fractured his elbow as well as his wrist, and, after a series of rehab assignments, returned to San Antonio for 10 games in August.

[38] In late July, after hitting .316 with 23 stolen bases, Jankowski was promoted to the Triple-A El Paso Chihuahuas of the Pacific Coast League.

He singled in his first two at bats, joining John Sipin and Wiki Gonzalez as the third Padre in franchise history to record hits in his first two major league plate appearances.

First, on August 1, Wil Myers placed himself in a rundown situation as a distraction, allowing Jankowski to run home in the eighth inning of a 7–3 win over the Milwaukee Brewers.

[44] Jankowski began the 2018 season with the Chihuahuas, but was recalled to the Padres at the end of April, after Myers suffered an oblique strain in a game against the New York Mets.

[55] Jankowski, who honed his batting technique with the Chihuahuas hitting coach before his call-up, became the leadoff hitter for the Padres, where he could focus on getting on base and making contact with good pitches.

[44] During a spring training game in 2019, Jankowski suffered a fractured wrist while diving after a fly ball, and he was expected to miss three months of the season while recovering.

[44] On October 31, 2019, immediately after the conclusion of the MLB season, Jankowski was traded to the Cincinnati Reds in exchange for international bonus slot cash.

He told reporters there that he anticipated a new extra innings rule, in which teams began with a runner on second base, would help his chances of being named to the major league roster.

[63] He returned to the roster on September 30 for the postseason, and stole one base as a pinch runner in the first game of the 2020 National League Wild Card Series, against the Atlanta Braves.

[66] On May 30, after outfielder Roman Quinn suffered a ruptured Achilles tendon and was expected to miss the remainder of the 2021 MLB season, Jankowski was promoted from the Triple-A Lehigh Valley IronPigs to take his place in the roster.

Jankowski was caught stealing by Nationals catcher Alex Avila, a play which led to booing from Phillies fans at Citizens Bank Park.

He broke his hand on May 25 after making a diving catch to rob Giants catcher Joey Bart of a hit, and was placed on the injured list expected to miss six to eight weeks.

[88] In his first career playoff at-bat, Jankowski was robbed of a home run by Astros outfielder Kyle Tucker in Game 6 of the 2023 American League Championship Series.

Jankowski recorded two hits, two RBI and two runs scored while making a sliding catch that narrowly avoided colliding with Marcus Semien to end the seventh inning.

In the ninth inning, Jankowski singled to center field, then quickly stole second base before Andy Parrino drove the run in, pushing Team USA to the finals.

[105] In 2016, while serving primarily as a relief in right field for starter Matt Kemp, Padres manager Andy Green said that "Travis has more range than 99.9 percent of all outfielders in major league baseball".

[109] While playing with the Reds in 2020, Jankowski was also frequently mistaken for retired pitcher Bronson Arroyo due to their similar frames and long blond hair.