Directed by John Tiffany, the eight-time Tony winning musical opened at the Phoenix Theatre in April last year, where it recently extended booking to 4 July 2015.
To celebrate its first birthday in the West End, St Patrick's Day, and Darvill's first performance, Once will join forces with the charity Oxfam for a gala night on 17 March 2014.
Lauren Laverne, a supporter of Oxfam's Mother Appeal, said: "It's great that the West End production of Once and Oxfam are teaming up to raise vital funds for the Mother Appeal. The musical could not be a better example of how a struggling mother strives to give her young daughter the best in life."
Based on the Oscar-winning film, Once centres on an Irish busker and a young Czech mother who meet through a shared love of music.
Arthur Darvill recently completed a run in the Broadway production. In London his previous theatre roles include Our Boys at the Duchess Theatre, Soft Cops for Royal Shakespeare Company, Doctor Faustus at Shakespeare's Globe, Been So Long for Young Vic and Swimming with Sharks at the Vaudeville Theatre.
Darvill played the Doctor's companion Rory in Doctor Who for two years and more recently he played Reverend Paul Coates in ITV's award-winning Broadchurch and The Duke of Buckingham in The White Queen for the BBC.
Once has book by award-winning Irish playwright and screenwriter Enda Walsh. Based on the 2007 motion picture written and directed by John Carney, music and lyrics are by Academy Award-winning Glen Hansard and Markéta Irglová who, for "Falling Slowly", won the Oscar for Best Original Song.
Scenic and costume designs are by Bob Crowley, with lighting by Natasha Katz, sound by Clive Goodwin, musical supervision and orchestrations by Martin Lowe and movement by Steven Hoggett.