The Spanish baritone was best known as one fourth of the classical crossover group that first emerged in 2004.
Carlos’ fellow Il Divo singers – David Miller, Sébastien Izambard and Urs Bühler – broke news of his death on Sunday as they paid tribute to him on Twitter.
They wrote in a statement: “It is with heavy hearts that we are letting you know that our friend and partner, Carlos Marin, has passed away. He will be missed by his friends, family and fans. There wiIl never be another voice or spirit like Carlos.
“For 17 years the four of us have been on this incredible journey of Il Divo together, and we will miss our dear friend.
“We hope and pray that his beautiful soul will rest in peace. With Love ― David, Sebastien and Urs.”
On Thursday, the group shared news that Carlos had been admitted to hospital and said they were “hoping and praying for a speedy recovery”.
His cause of death has not been confirmed.
Carlos had been on stage performing with Il Divo earlier this month, though the rest of their December UK tour dates were later postponed by a year “due to illness”.
Carlos rose to fame in 2004 when Il Divo’s self-titled debut album hit number one, after the group were formed by Simon Cowell and signed to his Syco record label.
The group have since gone on to release another nine studio albums, and have sold over 30 million records worldwide.
Carlos was previously married to French-born singer Geraldine Larrosa – known by her stage name Innocence – from 2006 to 2009.