Gymnastics career
Marinov competed at his first senior-level Russian Championships in 2022 and won the horizontal bar title.
At the 2024 BRICS Games, Marinov competed against international gymnasts for the first time and won the all-around competition, ahead of Olympic champion Artur Dalaloyan. He then won another gold medal in the parallel bars final. He also won silver medals on the vault and horizontal bar and won a bronze medal on the rings.
Marinov was approved by the International Gymnastics Federation to compete internationally as an Authorised Neutral Athlete in 2025. He won the all-around title at the 2025 Russian Championships. In the apparatus finals, he also won the floor exercise and parallel bars titles and won a bronze medal on the vault. At the 2025 World Championships, he advanced into the all-around final and finished seventh. He then won the bronze medal in the parallel bars final, behind China's Zou Jingyuan and Japan's Tomoharu Tsunogai. Additionally, he placed seventh in the vault final and eighth in the horizontal bar final.
Marniov competed at the 2026 European Championships alongside Mukhammadzhon Iakubov, Arsenii Dukhno, Savelii Sieedin, and Ilia Zaika. On the first day of competition, Marinov helped Russia (competing as World Gymnastics 2) qualify to the team final in first place and individually he won bronze in the all-around behind Illia Kovtun and Dukhno.
Marniov was selected to represent Russia at the 2026 World Championships alongside Dukhno, Sergei Naidin, Sieedin, and Zaika. The entire Russian delegation ran into visa issues as the Netherlands had not granted them prior to their initial scheduled departure date. On October 12, five days before the official competition start date, Dukhno, Naidin, and women's team member Alena Glotova were granted visas. As a Bulgarian citizen, Marniov was able to travel to the Netherlands with them using his Bulgarian passport. The rest of the men's team were granted visas but were not able to travel the Netherlands in time for podium training. During the qualification round, Marinov helped Russia qualify to the team final and individually he qualified to the all-around and parallel bars finals. During the team final, he performed on four of the six apparatuses, helping Russia win the silver medal and qualifying them a whole team to the 2028 Summer Olympics.
