At the age of 12, he lent his voice to the main character of the German radio drama adaptation of Oscar and the Lady in Pink, a novel by Éric-Emmanuel Schmitt.

[5] In 2013, Schümann starred as the manipulative teenager Alev El Quamar in Gaming Instinct, a drama film adaptation of Juli Zeh's novel of the same name.

[10] In 2016, he starred as the love interest of Louis Hofmann in Center of My World, a gay coming-of-age drama dubbed by The Hollywood Reporter as "a beguiling teen romance",[11] while described by The Guardian as "genuinely cute".

[13] In 2017, Schümann was cast as the lead in the critically acclaimed dystopian drama Godless Youth [de], opposite of Jannis Niewöhner.

They keep their affair a secret in fear of Martin being sent to a concentration camp over Paragraph 175, a German law that made homosexual acts a crime.

He portrayed model and kickboxer Danny Taylor, a survivor of severe child sexual abuse who was infected with HIV by his father.

[18] On 26 December 2020, Schümann published a photo on Instagram with his partner Felix Kruck, a move interpreted by the international media outlets as his public coming out as gay.

[19] In 2021, Schümann criticized the coming out narrative and explained that he had never made a secret of his homosexuality, stating that he only published the photo of his partner "as a signal of support for the LGBTQ community.

[21] On the International Holocaust Remembrance Day on January 27th, 2023, he gave a speech in the German Parliament officially commemorating the LGBTQ victims of the Nazi regime for the first time in the country's history.