After graduating from the university in 1988, he joined Japan Soccer League side Nissan Motor F.C. (current Yokohama F. Marinos). He contributed to the club winning the Emperor's Cup twice in 1988 and 1989. When Japan's first-ever professional league J. League started, Shimizu S-Pulse was founded in his local city. He joined the club in 1992 and re-united with his high school teammates Oenoki and Horiike. He helped the club to win the J. League Cup in 1996. He retired as a Shimizu player after the club won the second stage of the J. League 1999 season. He played 207 league matches and scored 45 league goals in 7 seasons at Shimizu.
He was capped 27 times and scored 4 goals for the Japanese national team between 1989 and 1995. His first international appearance came on January 20, 1989 in a friendly against Iran in Teheran. He scored for the first time for his country on June 11, 1989 in a 1990 FIFA World Cup qualifier against Indonesia at Nishigaoka Soccer Stadium in Tokyo. He was a member of the Japan squad who participated in the AFC final qualifying stage for the 1994 FIFA World Cup. In the crucial last match, Hasegawa was substituted in the 59th minute by Masahiro Fukuda and watched from the bench a late Iraqi equaliser dashed Japan's hope to qualify for the finals in the U.S.A., the match that the Japanese fans now refer to as the Agony of Doha.
After retiring from the game, he started working as a pundit for national television NHK. He was also installed as the general manager of two university clubs, Hamamatsu University S.C. and Fuji Tokoha University F.C. (2000–2001). He became the manager of Hamamatsu University S.C. and lead them to win the Tokai University League title and the Shizuoka Prefectural qualification for the Emperor's Cup. He acquired the S-class coaching license that was required to manage a J. League club in 2004 and became the manager of his old club S-Pulse in 2005. The club struggled and narrowly escaped relegation in the 2005 season but they fought back strongly in the 2006 season and finished 4th in the league; a position equaled in 2007. In 2008 Hasegawa led S-Pulse to the final of the Nabisco Cup and a fifth placed finish in the league, a placing which included them being the strongest performing team in the second half of the season. He was rewarded with an extended contract which will keep him at S-Pulse until 2010. He left Shimizu after he led the club to the final of 2010-11 Emperor's Cup when his contract was expired.
Hawegawa was appointed as a manager at Gamba Osaka in 2013.
In popular manga and anime series Chibi Maruko-chan, a boy called Kenta kun occasionally makes an appearance. He loves football and is a classmate of title character Chibi Maruko. Momoko Sakura, the author of the manga, created this character after Hasegawa. Sakura and Hasegawa attended the same primary school during the same period.