Marlon took up riding at age four in Fortaleza, Brazil. He was influenced by his grandfather Darcy and his father Mario, who built a riding school from scratch. His parents Mario and Maristela developed a project called Equitakids in Maceio, Brazil, to get children started in sport at an early age.
In 1994 his father Mario attempted to enter the eventing competition of the 1995 Pan American Games in Argentina. He was ultimately unsuccessful, but Zanotelli and his three brothers lived in a truck for a year while Mario competed at various events. Zanotelli also struggled with little money when he began competing. "One time we went to a competition in Recife, and since we couldn't afford the hotel, we slept in the car with the air conditioning on. And one time in Belo Horizonte, we slept in a shed."
After riding for Helio Pessoa in Guatemala and Yuri Mansur in Sao Paulo, Brazil, he went to Europe to ride under Belgian jumper Ludo Philippaerts in April 2008. "I thought I would get there and just immediately participate in contests and ride good horses but I had to earn my space, which was a very good experience.
His motto is, "things happen at the right moment for the right reason."
Competed in the 2014 World Championships
2019 LGCT Rome Grand Prix Silver Medalist with VDL Edgar M
2019 LGCT Super Grand Prix Qualifier (Rome)