The 30-year-old previously played for the Spanish club U.E. Llagostera.
Marcos is an academy product of Spanish giants Real Madrid. He only made one appearance for Real's senior side in the 2009-10 season before being loaned out.
"I'm very excited about this new stage in my career. I am looking forward to play for the Delhi Dynamos FC. I am sure ISL will be an enriching experience for me and I hope to take the maximum from it. My aim is to win the title this season with my new club," Marcos said in a release.
"I intend to learn a lot from head coach Gianluca Zambrotta. He's got immense experience, I am looking forward to working with him and the rest of the team."
Zambrotta was enthusiastic about his team's latest signing.
"Marcos is a very talented and experienced player. He has played against the top-flight clubs of Europe and his experience will be very useful for the team. He has an excellent tactical approach towards the game," said Zambrotta.