Among the mourners were Dixies showband stalwarts Sean Lucey and Joe McCarthy.
Friends and admirers of the hugely popular entertainer lined the streets as the coffin made its way from the Jerh O’Connor Coburg Street funeral home to St Patrick’s Church on Lower Glanmire Road.
Mr O’Brien, one of this country’s first indigenous pop stars in the 1960s and 1970s, will be buried in St Finbarr’s Cemetery after 1pm funeral mass today.
Mr O’Brien was found dead at his home in Cork city last Thursday.
He joined the Dixies as a singer and guitarist in 1961.
The band achieved their biggest hit in 1968 when Little Arrows went to number one in the Irish charts and stayed there for a record-breaking 26 weeks.
Four months ago Mr O’Brien was one of those who paid tribute to Joe Dolan on his sudden death.
Mr O’Brien is survived by his five children, Brendan, Conor, Trish, Aideen and Sinead, all of whom are living in Canada.