Irabu was born on May 5, 1969 in Hirara (present: Miyakojima), Okinawa, Japan (then administered by the government of the United States). His father was a U.S. Air Force meteorologist named Steve Thompson, married to a woman in the United States at the time. Thompson, who had been redeployed to Vietnam before his son’s birth, briefly visited young Hideki and his mother a year later, but they would not again meet until after Irabu reached the U.S. major leagues. Hideki’s mother, Kazue, a native of Miyako, later married a restaurateur, Ichiro Irabu, from Osaka. Irabu raised Hideki as his son in Amagasaki, Hyōgo Prefecture.

Irabu pitched for the Lotte Orions, who later became the Chiba Lotte Marines, of the Pacific League from 1988 to 1996. He was known as a high-speed pitcher and in 1993, he threw a 158 km/h (98 mph) fastball against Kazuhiro Kiyohara of the Seibu Lions. This was the fastest clocked pitch in all of Japanese Professional Baseball (NPB) until 2005, when the record was broken by Marc Kroon of the Yokohama BayStars.

Irabu led the Pacific League in wins in 1994 (15) and in ERA in 1995 and 1996 (2.53 & 2.40, respectively). He also led the Pacific League in strikeouts in 1994 and 1995 (239 & 167, respectively).

In 1997, the San Diego Padres purchased Irabu’s contract from the Chiba Lotte Marines. The criticisms of this sale from other MLB teams, who wished to bid on Irabu, led to the creation of the posting system currently used by Japanese and MLB teams. Irabu, however, refused to sign with the Padres, saying he would only play with the Yankees. For the negotiating rights to Irabu, the Yankees offered the Padres a choice of one from a list of players including Brian Boehringer, David Weathers, Chris Cumberland, Andy Fox and Matt Luke. The Padres eventually included him as a player-to-be-named-later in a trade that involved Homer Bush and Irabu going to the New York Yankees in exchange for Rafael Medina, Rubén Rivera, and $3 million in cash. The Yankees signed Irabu to a $12.8 million, four-year contract, and after only eight minor league appearances, the Yankees put him in their rotation.

Irabu made his highly publicized debut on July 10, 1997, drawing almost twice as many fans that night as they averaged for weeknight games. He played with the Yankees from 1997 through 1999, winning two World Series rings (1998, 1999) despite only pitching in one postseason game and having no postseason decisions. George Steinbrenner publicly expressed disgust at his weight, at one point calling him a “fat pussy toad” after he failed to cover first base on a ground ball during a spring training game. Steinbrenner refused to let Irabu accompany the team to Los Angeles, but two days later, Steinbrenner apologized and allowed Irabu to join the team.

1998 was Irabu’s best season in MLB, featuring career bests in games started (28), complete games (2), innings pitched (173), wins (13), and ERA (4.06). Despite his inconsistency, Irabu was twice named the American League’s Pitcher of the Month: in May 1998 and June 1999.

After the 1999 season, he was traded to the Montreal Expos for Ted Lilly, Christian Parker, and Jake Westbrook. He started only 14 games for the Expos in 2000 and 2001, pitching 71⅓ innings with a 6.69 ERA and only 2 wins against 7 losses.

In 2002, he signed as a free agent to pitch for the Texas Rangers as a closer.

Before the 2004 season, he pitched 2004 MLB Japan Opening Series exhibition games against the Tampa Bay Devil Rays.

On August 20, 2008, Irabu was arrested on the suspicion of assaulting the manager of a bar in Umeda, Osaka. He was upset that his credit card was not accepted in the bar. At the time of the suspected assault, Irabu had consumed at least 20 glasses of beer. Irabu admitted to the assault, the bartender sustained no injuries, and Irabu paid the bill with another credit card.

In April 2009, Irabu had come out of retirement and made a contract with Long Beach Armada of the independent Golden Baseball League. He posted a 5–3 record in 10 starts, with an ERA of 3.58. In 65 innings Irabu struck out 66 batters while walking just 19. In August, he announced his intention to return to the Japanese professional leagues, and began playing for the semi-professional Kōchi Fighting Dogs.

Irabu was arrested for DUI on May 17, 2010, in Redondo Beach, California. The press release of his arrest stated he resided at the time in Rancho Palos Verdes.

Irabu was found dead in his home in Los Angeles on July 27, 2011. He was reported to have hanged himself. He left behind his wife and two children. Irabu’s autopsy showed he was inebriated at the time of his death with both alcohol and Ativan in his system. He was reportedly despondent because his wife had taken their two daughters and left him.