There were tears and applause as Benn's coffin was driven from the Houses of Parliament in London to St Margaret's Church across the road, his coffin topped with red roses.
A Labour cabinet minister in the 1960s and 1970s, Benn was a widely respected orator who clashed with his party's leadership over its drift away from the radical socialism he espoused.
Aged 88, Benn died peacefully at his west London home on March 14, surrounded by his family.
"We give you thanks for Tony's passion for justice, for his integrity and tenacity in refusing to compromise in striving for what he believed to be right," Reverend Rose Hudson-Wilkin, the parliament speaker's chaplain, said in a prayer.
After the service, socialist anthem "The Red Flag" was played.
Well-spoken with colourful gesticulations, Benn was never too far away from his pipe and a huge mug of tea.
Benn forced a change in the law allowing hereditary members of parliament's upper House of Lords to renounce their titles, after he was disqualified from his seat in the elected Commons on inheriting his father's Viscount Stansgate title in 1960.
Benn's coffin had spent the night in parliament in its 13th-century Chapel of St Mary Undercroft, an honour given to former prime minister Margaret Thatcher in April last year.
His funeral was to be followed by a private family cremation later today. A memorial meeting is planned for later this year.
