Kato was born in Saitama, and started racing miniature bikes at an early age, becoming a four-time national champion in the Japanese pocket-bike championship.
He began road racing in 1992, and entered his first Grand Prix in 1996, as a wild-card rider. In the 250 cc class, he finished in third at his debut on his home circuit at Suzuka. The next year, he won the Japanese Championship, and again entered the Japanese Grand Prix with a wild card, winning the race at this occasion.
In spite of these successes, Kato didn't ride his first full Grand Prix season until 2000, when he started in the 250 cc, riding a Honda. He won four races that season (of which two in Japan), and placed third in the championship. In 2001, he literally dominated the 250 cc championship. He won no less than 11 races - a record - and easily won the title.
The following season, Kato moved up to the MotoGP class (formerly 500 cc). In spite of rider a weaker two-stroke bike the first half of the season, Kato performed reasonably well.
In the first race of the 2003 season, at his favourite Suzuka circuit, Kato crashed hard, and sustained head, neck and chest injuries. He died two weeks later from his injuries.