In 1991, Wada and his family moved to Izumo, Shimane Prefecture, Wada’s father’s hometown. Wada enrolled in Shimane Prefectural Hamada High School in Hamada upon graduating from junior high, leading them to the 79th National High School Baseball Championship in the summer of his second year of high school (the equivalent of eleventh grade in the United States) in 1997. His team faced Akita Commercial High School, led by current Tokyo Yakult Swallows ace Masanori Ishikawa, in the first round, but Wada walked that very Ishikawa with the bases loaded in the bottom of the ninth inning and suffered a walk-off loss.

Wada secured a spot in the Hawks’ starting rotation from his rookie year (2003), making his professional debut in a regular season game against the Osaka Kintetsu Buffaloes on April 1 (he gave up five runs in 6 ⁄3 innings). He earned the first win of his career against the Seibu Lions on April 8, pitching six shutout innings, and recorded his first career complete game win (a shutout) against the Chiba Lotte Marines on April 16. Overall, he finished the year with a 14-5 record, 3.38 ERA and 195 strikeouts (second only to young Lions right-hander Daisuke Matsuzaka’s 215), earning Pacific League Most Valuable Rookie honors. He also played an instrumental role in the Hawks’ league title and subsequent Japan Series championship, pitching a complete game win as a rookie for the first time in Japan Series history in Game 7 of the series. He played in the 2003 Asian Baseball Championship (which also functioned as the Asian qualifying tournament for the 2004 Athens Olympics) as a member of the Japanese national team in November, pitching 5 ⁄3 shutout innings against South Korea in the final game of the tournament to clinch a berth in the upcoming Olympic Games.

Wada played in the 2004 Athens Olympics, contributing to Japan’s bronze medal finish in the tournament by earning two wins against Canada (one in the preliminary round, the other in the bronze medal match) while holding them to two runs over twelve innings. However, he fell victim to a so-called sophomore slump in the regular season, going 10-6 but racking up a 4.35 ERA and striking out just 115 batters (despite this, his batting average against was a league-best .228).

In 2005, Wada was named the starter for the Hawks’ season opener for the first time in his career, taking the mound against the Fighters on March 26 and holding them to one run over 7 ⁄3 innings while striking out eight en route to the win (though he required 135 pitches). He finished the year with a 12-8 record and a much-improved 3.27 ERA, becoming the first pitcher to record double-digit wins in each of his first three seasons in Hawks franchise history since Tadashi Sugiura accomplished the feat in 1960.

Though Wada improved on his ERA still more by lowering it to 2.82 in the 2007 season, he was plagued by poor run support and went 12-10 for the year. He pitched the most innings (182) and amassed the most strikeouts (169) since his rookie campaign and became the only active pitcher other than the aforementioned Masanori Ishikawa (and the first in Hawks franchise history since Sugiura) to record double-digit wins in each of the first five seasons of his professional career.

The rehab that Wada had to undergo following the elbow surgery kept him from making his first start of 2008 until April 6, roughly two-and-a-half weeks into the season. Despite the slight setback, he started the season of well, putting up eight wins before the All-Star break and garnering selection to the Japanese national team that would play in the 2008 Beijing Olympics. However, he did not pitch as had hoped in the Olympics, giving up six runs (five earned) in two starts en route to a 4.82 ERA over 9⅓ innings (albeit while striking out 13) and being one of the factors in Japan’s disappointing fourth-place finish behind South Korea, Cuba and the United States.

In 2009, Wada was named to the national team’s preliminary roster for the upcoming World Baseball Classic along with teammates first baseman Nobuhiko Matsunaka, starter Toshiya Sugiuchi, closer Takahiro Mahara and shortstop Munenori Kawasaki. However, though he took part in the training camp held in Miyazaki in mid-February, he and Matsunaka were cut from the final 28-man team before the tournament.

Wada was selected for the All Star Series in 2010 and started game 1. His team-mate Sugiuchi Toshiya started game 2. They lead the Pacific League in wins through most of the season. It was their fine form that carried the Hawks to the league title in 2010 as the rest of the team’s starters struggled. Wada was named Pacific league MVP for the 2010 season, helping the Hawks win the regular season pacific league pennant.

On December 14, 2011, Wada agreed to a two-year deal with the Orioles, including an option for a third year.

Wada underwent Tommy John surgery on May 11, 2012 due to a partially torn ligament in his left elbow and spent the rest of the 2012 season on the disabled list. He started the 2013 season on the 60-day disabled list, and was expected to join the Orioles around June 1, 2013. He started a rehab assignment with the Triple-A Norfolk Tides on May 16. On June 14, he was activated from the 60-day disabled list and optioned to Norfolk.

Wada signed a minor-league contract with invitation to spring training with the Chicago Cubs on January 24, 2014, but he was released on March 23, 2014. He re-signed with the Cubs on another minor league contract the next day. His contract was selected from the Triple-A Iowa Cubs on June 22, and he was optioned to Iowa. He was recalled by the Cubs on July 8, and started the second game of that day’s doubleheader against the Cincinnati Reds.

In 2014 Wada compiled a 4-4 record and a 3.25 ERA. His strongest outing came on August 24, 2014 when he took a no-hitter into the seventh inning against the Baltimore Orioles. He was removed from the game after giving up a solo home run, the only hit he allowed in the contest. The Cubs won 2-1, and Wada was credited with the win. He was signed to a one-year $4 million contract after the season. Wada made seven starts for the Cubs during May and June 2015 before suffering a shoulder injury, he returned in September but pitched out of the bullpen.

Wada returned to Japan, signing with the Fukuoka SoftBank Hawks of Nippon Professional Baseball for the 2016 season. In 2016 season, Wada finished the regular season with a 24 Games pitched, a 15–5 Win–loss record, a 3.04 ERA, a 157 strikeouts in 163 innings. And he was honored with the 2016 Pacific League the most wins Champion and 2016 Pacific League Winning percentage leader.

On May 22, Wada had left elbow surgery and spent three months in rehabilitation. On August 27, he made a comeback and pitched against the Chiba Lotte Marines, and recorded 1,500 strikeouts in total. In 2017 season, he finished the regular season with a 8 Games pitched, a 4–0 Win–loss record, a 2.49 ERA, a 34 strikeouts in 47 innings. On November 1, he pitched against the Yokohama DeNA BayStars as a starting pitcher in the 2017 Japan Series.

On June 5, Wada made a comeback and pitched Interleague play (NPB) against the Chunichi Dragons. In 2019 season, he finished the regular season with a 12 Games pitched, a 4–4 Win–loss record, a 3.90 ERA, a 45 strikeouts in 57 2/3 innings. On October 23, he pitched against the Yomiuri Giants as a starting pitcher in the 2019 Japan Series, and won the game for the first time in 16 years since the 2003 rookie year.