Patriarch Daniel joined hundreds of other mourners at the service for Claudiu Petre at St Dumitru church.
Thirty six year old Petre, was praised after he entered the Colectiv nightclub while it was on fire to rescue a woman then went back to find other survivors. He was never seen alive again.
The blaze killed 32 and dozens remain in hospital. It is claimed a spark ignited flammable foam. The nightclub's owners are still being questioned by police.
During his funeral which lasted two hours, Mr Petre was praised for his "bravery, altruism and dedication".
His friend Valentin Diaconescu said: "He was - no he is - a wonderful person, cheerful, he helped everyone, he was the life and soul of the party.
"He is all of those things. I don't want to talk about him as if he's gone."
The Romanian Orthodox Church has been criticised for failing to address public grief unlike clerics from other churches.
The surprise visit by Patriarch Daniel saw him enter the church by a back gate to avoid mourners who may have been critical of him.