Yamamoto was born in Takarazuka, Hyogo; his father died shortly after his birth, and he and his two older sisters were raised by their mother, who sold Persian carpets.

He appeared in dozens of films, including Battle Royale (2000) and Moon Child (2003), winning a Blue Ribbon Award for Best Supporting Actor for the latter.

Yamamoto, a resident of Tokyo, flew to Saga Prefecture in July and attempted, along with a local citizens' group, to enter the governor's office to protest the restart of a power plant.

[4] The scene was broadcast on television, and the Saga District Public Prosecutors Office considered pressing charges against Yamamoto.

The Huffington Post reported that the action may have violated the Constitution of Japan, since the Emperor is not allowed to involve himself in political issues.

[11] The Japanese Communist Party chairman Kazuo Shii inferred that Yamamoto "didn't understand the Constitution".

[12] Various political leaders expressed their anger and disappointment in Yamamoto's alleged abuse of his legislative position,[13] as well as Takeshi Kitano, who called the incident "somewhat of an insult".

In December 2013, he promised he would mobilize a million people to lay siege to the National Diet in protest of the State Secrecy Law.

His campaign was mainly based around a pledge to cancel the 2020 Summer Olympics, and to also establish a 100,000 yen direct cash relief handout program as a part of Tokyo's response to the COVID-19 pandemic.

Reiwa Shinsengumi also withdrew seven candidates as part of the pact, meaning over 40% of its planned slate would end up not running.

In 2023, Liberal Democratic Party lawmakers physically held Yamamoto back as he attempted to fling himself at members desks to block an anti-refugee bill in the House of Councilors.