Heavy rain fell as international stars gathered for the glitzy ceremony in Covent Garden, one night after the Irish film industry celebrated its talent in Dublin’s Burlington hotel.
Although she did not win the BAFTA, Ms Ronan, nominated for leading actress for her role in Peter Jackson’s fantasy movie, The Lovely Bones, held her own on the red carpet.
Dressed in a strapless, white ruffled number, she said it was “kind of surreal” to be there.
“I didn’t know what to expect and it’s still all taken me by surprise,” she said.
Possibly the youngest star at just 15, Ms Ronan, who was dressed head to toe in Burberry – as on Saturday at the IFTAs – wore a pretty white ruffled shoulderless dress, with pebbled bracelets.
“The Lovely Bones has been a bit of a whirlwind,” she said. “It’s really taken me all over the world.
“It’s great that it’s brought me here. I’ve never been before.”
Ms Ronan lost out in the actress category to Carey Mulligan for her role in An Education.
Iraq thriller The Hurt Locker beat off competition from blockbuster Avatar to win best film while Colin Firth took the best actor gong for his role in The Single Man.