While representing the Philippines as an amateur, he won a silver medal at the 2019 World Championships and bronze at the 2020 Summer Olympics, both in the middleweight division.

Marcial won the 2011 International Boxing Association (amateur) Junior World Championships in three years after he took up training for the first time.

"[4] At the 2019 AIBA World Boxing Championships in Ekaterinburg, Russia, Marcial settled for silver in the middleweight category losing to Russian boxer Gleb Bakshi in the final bout.

[10] In July 2020, Marcial turned pro and signed in with MP Promotions although he has pledged to continue to represent the Philippines in international amateur competitions such as the Southeast Asian Games and the Summer Olympics.

[11] Marcial signed with the Premier Boxing Champions (PBC) and his professional match will be a four-round middleweight bout against Andrew Whitfield from Lewiston, Idaho.

[17][18] Eumir denies the claim insisting that he was the abuse victim and has been estranged with his wife before the 2024 Summer Olympics and that the alleged mistress is merely a friend.