[4] He went on to play for the Takarazuka Boys while attending Itami Municipal Matsuzaki Junior High School, being used at both pitcher and catcher because of his strong throwing arm.

Armed with a fastball that sat in high-80s and a hard slider, he led his team all the way to a championship in the 87th National High School Baseball tournament held at Koshien Stadium in the summer of his second year (eleventh grade).

[citation needed] In the rematch that ensued the next day, Tanaka again came on in relief in the bottom of the first, but Tomakomai High lost to Waseda Jitsugyo despite his pitching the remaining 71⁄3 innings of the game.

[citation needed] Tanaka, dealing with intestinal inflammation, threw 742 pitches in 522⁄3 innings (six appearances) in the tournament, striking out 54 and walking 20 with a 2.22 earned run average (ERA).

[9] On September 25, in the 2006 NPB high school draft, the Hokkaido Nippon Ham Fighters, Orix Buffaloes, Yokohama BayStars and Tohoku Rakuten Golden Eagles all selected Tanaka with their first-round picks.

[citation needed] Tanaka was named to the Eagles' ichigun (Japanese equivalent of "major league") roster during Spring training of his rookie year, and made his professional debut on March 29, 2007, against the Fukuoka SoftBank Hawks as the starting pitcher, but gave up six runs on six hits and a walk in 12⁄3 innings.

He became the first pitcher since Yu Darvish to throw a complete-game shutout as a rookie out of high school on June 13 in an interleague game against the Chunichi Dragons.

[14] His 196 strikeouts were the second-most by any pitcher in either league (Pacific or Central) and the fourth-most as a rookie out of high school in Japanese professional baseball history.

[18] Tanaka was able to make only 24 starts (as opposed to 28 in his rookie season), missing playing time because of both a brief rehab stint in the minors due to inflammation in his shoulder[19] and his participation in the 2008 Beijing Olympics as a member of the Japanese national team.

The Eagles eventually won in walk-off fashion in the twelfth inning, finishing one game ahead of the Hawks for fifth place in the regular season standings.

[25] On September 13, 2013, Tanaka set a new NPB record with his 21st consecutive win in the 2013 season in a 6–2 complete game victory over the Orix Buffaloes at home in Sendai at Kleenex Stadium.

[32] Tanaka made his Major League debut on April 4, 2014, against the Toronto Blue Jays and gave up a home run to the first batter he faced, ex-Yankee Melky Cabrera.

In June, Tanaka recorded his 100th strikeout of the season in a complete game against the Seattle Mariners; his bid for a shutout was ended when former Yankee Robinson Canó hit a two-run home run in the ninth inning.

At the behest of several doctors, Tanaka received a PRP shot from Yankees' head team physician Dr. Christopher Ahmad[38] and rested his elbow for 6 weeks instead of having Tommy John surgery to repair his UCL.

The injury combined with his poor first outing led many in the sports media to speculate that Tanaka should undergo Tommy John surgery against the wishes of his doctors.

[45] Tanaka was diagnosed with a Grade 1 hamstring strain on September 20, sustaining the injury during an interleague game against the New York Mets when running to first base after a bunt attempt.

[46] Tanaka's season ended with a 3–0 loss to the Houston Astros in the American League Wild Card game, in which he pitched five innings and allowed two earned runs.

[61] Making the Opening Day start against the Tampa Bay Rays on April 2, Tanaka lasted only 2+2⁄3 innings, allowing a career-high seven earned runs as the Yankees lost by a score of 7–3.

[65] On June 23, Tanaka started against fellow Japanese pitcher Yu Darvish for the first time in the United States, outdueling him by throwing eight shutout innings and striking out nine in a no-decision.

[77] On September 29 against the Blue Jays, his final start of the regular season, Tanaka again set a new career-high by striking out 15 batters, tied with Stephen Strasburg for the most single-game strikeouts in 2017.

[80] However, he faced Keuchel again in Game 5, this time earning the win as he pitched seven shutout innings, striking out eight to help the Yankees take a 3–2 series lead.

[81] On November 3, Tanaka announced that he would not exercise the opt-out clause in his contract, instead staying with the Yankees for the remaining three years and $67 million left on his original deal.

[82] Tanaka's first start of 2018 went smoothly as he retired 13 batters in a row, struck out eight, and allowed one run, which was a solo homer by Randal Grichuk in 6+ innings as the Yankees won 4–2.

[83] While playing at Citi Field against the Mets on June 8, Tanaka scored his first career run after a sacrifice fly from Aaron Judge, but shortly after, he left the game after his hamstrings grew stiff.

[88] On July 6, Tanaka was named to the 2019 Major League Baseball All-Star Game as an injury replacement for Toronto Blue Jays pitcher Marcus Stroman.

On July 4, 2020, in a Yankees simulated game, Tanaka was struck in the head by a line drive off of the bat of Giancarlo Stanton and suffered a mild concussion.

In March 2021, months after Tanaka had already returned to Japan, Yankees General Manager Brian Cashman commented: (It is) heartbreaking to hear any of these stories that come out.

He pitched in the semi-finals against the United States, giving up a triple to Jimmy Rollins but striking out David Wright to end the inning, contributing to Japan's second consecutive championship in the tournament.

Tanaka was highly expected to be the staff ace of Team Japan in the 2013 WBC, but poor form in the build-up to the tournament led to concern over his performance.

[114] During the game in which he set a new Japanese professional baseball record of 16 consecutive victories in one season, cheer banners of the same color scheme were distributed among the spectators.