Yamamoto began his racing career in 1994 at the Suzuka Circuit Racing School karting programme, progressing through the Japanese domestic formulae ladder over the following decade. His advancement through national series eventually brought him to the attention of Super Aguri F1, who installed him as their test and third driver for one weekend — the 2005 Japanese Grand Prix — within the Jordan Formula One team as part of his preparation.
On 8 June 2006, Yamamoto formally joined Super Aguri F1 as test and third driver, assisting race drivers Takuma Sato and Franck Montagny on Friday free practice sessions. When Montagny was moved back to test duties ahead of the German Grand Prix at Hockenheim, Yamamoto stepped into the second race seat.
His debut was difficult — mechanical failure and a stalled engine left him with just one completed lap across his first two races. He also damaged one of the team's SA06 chassis in a crash during free practice at Hockenheim. At the Turkish Grand Prix he outqualified Sato for the first time before spinning out of the race.
Yamamoto's most consequential moment of 2006 came at Monza, where a tyre delamination during qualifying sent debris onto the circuit. Fernando Alonso punctured a tyre on the debris while on a flying lap, which contributed to a chain of events that resulted in the championship leader being penalised and dropping five grid positions for the race. Yamamoto himself retired from the Italian Grand Prix with hydraulic problems.
He recorded his first finish at the Chinese Grand Prix, crossing the line sixteenth despite being four laps down. Yamamoto finished the season with three consecutive classified results and set the seventh-fastest lap at the 2006 Brazilian Grand Prix. Despite this upturn in form, he lost out to Anthony Davidson for the second Super Aguri race seat in 2007 and reverted to test driver duties, combining that role with a GP2 campaign with BCN Competicion.
With Christijan Albers departing Spyker F1 after the 2007 British Grand Prix, Yamamoto was confirmed as his replacement from the Hungarian Grand Prix onwards, having been loaned from Super Aguri. Markus Winkelhock had filled the seat for the intervening European Grand Prix in the meantime.
At Hungary, Yamamoto crashed out on lap four. For the remainder of the season he finished every race in last position except two: at the Japanese Grand Prix he came home ahead of Jarno Trulli, and at the Brazilian Grand Prix he was involved in a first-lap collision with Giancarlo Fisichella, which removed him from the results.
Yamamoto was announced as a Renault F1 test driver in February 2008, though his role was limited to public demonstrations rather than circuit testing. Mid-season, ART Grand Prix drafted him into the GP2 Series in place of the underperforming Luca Filippi. Yamamoto scored his first-ever points in any racing class outside Japan with a fourth-place finish in the sprint race at the Hungaroring.
He retained his ART seat for the 2008-09 GP2 Asia Series, where he finished ninth in the championship — somewhat in the shadow of teammates Nico Hulkenberg and Pastor Maldonado — but collected a podium at the opening round in Shanghai.
On 17 April 2010, Hispania Racing named Yamamoto as their test and reserve driver. He first appeared in free practice at the Turkish Grand Prix, where he set the slowest lap time of the session. He replaced Bruno Senna from the British Grand Prix, qualifying last and finishing twentieth. He then replaced Karun Chandhok at the German Grand Prix but retired after nineteen laps with an engine problem.
Yamamoto's 2010 season was interrupted when, at the Italian Grand Prix, his car struck a mechanic during a pitstop pit-exit — the crew member had been attempting to fix the radio connection and was hit by the rear wing. The mechanic was hospitalised for ten days. Yamamoto was stood down for Singapore, officially with food poisoning, and was replaced by Christian Klien. He returned for the Japanese Grand Prix, finishing sixteenth, and came fifteenth in Korea before Klien took his seat again for the final two rounds.
In 2011, Marussia Virgin Racing listed Yamamoto as their reserve driver for the first three races. He returned to competition briefly in 2015, substituting for Antonio Felix da Costa at the London ePrix with Amlin Aguri but failed to score points in either race.
Yamamoto entered the 2020 Super Formula Lights finale at Fuji with B-Max, scoring a best finish of seventh. Outside racing he built a career in medicine and social welfare, becoming head of a Japanese medical and social welfare corporation in 2012 with a focus on elderly care. He was elected to the Japanese House of Representatives on 31 October 2021, representing Tokai for the Liberal Democratic Party, serving until 2024.
Yamamoto's Formula One career was brief and frequently disrupted, but he remains notable as the driver whose 2006 Italian Grand Prix tyre failure had a tangible impact on that season's world championship fight between Fernando Alonso and Michael Schumacher. His post-racing transition into medicine and electoral politics in Japan is unusual among former Formula One drivers.