Mark Ishii is a Japanese voice actor born on November 21, 1991, in Chiba Prefecture. He is of Japanese and Filipino descent and spent four years of his early childhood in the Philippines. His inspiration to become a voice actor came during his junior high school days after playing the game.hack//G.U. and becoming a fan of the voice actor Takahiro Sakurai. Following his graduation from high school, he attended the Tokyo Announcement Academy to pursue his training.

Ishii's professional career began in 2013 with a role in the stage play Present◆5. He made his anime debut in 2014 with a small role in the film When Marnie Was There. That same year, he landed his first leading role as Bellri Zenam in the television series Gundam Reconguista in G, a performance that would become one of his signature parts.

He is widely recognized for several major anime roles. He voices Chrono Shindō, the protagonist of the Cardfight!! Vanguard G series, appearing in its various installments including Cardfight!! Vanguard G: Stride Gate-hen, Cardfight!! Vanguard G NEXT, and the original net animation mini vanguard Large. In the popular sports anime Haikyū!!, he provides the voice for Lev Haiba, a role he has reprised in multiple series and OVAs such as Haikyū!! Land VS. Air, Haikyū!! To The Top, and Haikyū!! Lev Kenzan!. More recently, he voices Hironobu Makita in the baseball anime Oblivion Battery, which began airing in 2024. Other notable roles include Kautz in the ONA Armor Shop for Ladies & Gentlemen and Tagi in the 2023 series Flaglia.

In 2019, Ishii was honored with the Best Rookie Actor Award at the 13th Seiyu Awards, recognizing his promising talent and early achievements in the industry. His career faced a temporary halt in December 2019 when he was diagnosed with an adjustment disorder and took a hiatus to focus on his health. He returned to voice acting in July 2020 after a seven-month break, initially signing with the agency Aksent before moving to his current agency, Mol+0, in 2023. He was previously married to fellow voice actress Atsuko Enomoto from 2016 to 2018.