Hamaguchi first gained international recognition with the film Happy Hour (2015) and continued with Asako I & II (2018).

[3][4][5] With Kō Sakai, he made a three-part documentary about survivors of the 2011 Tōhoku earthquake and tsunami, with Voices from the Waves being selected for the competition at the 2013 Yamagata International Documentary Film Festival,[6] and Storytellers winning the Sky Perfect IDEHA Prize.

[7] His next film, Happy Hour, was first developed while Hamaguchi was an artist in residence at KIITO Design and Creative Center Kobe in 2013.

[15] That same year, he released the film Gift, which uses the same footage as Evil Does Not Exist (though with a different story) and is accompanied by a live score.

In December 2023, alongside 50 other filmmakers, Hamaguchi signed an open letter published in Libération demanding a ceasefire and an end to the killing of civilians amid the 2023 Israeli invasion of the Gaza Strip, and for a humanitarian corridor into Gaza to be established for humanitarian aid, and the release of hostages.