Larn, 78, who lives on St Mary's in the Isles of Scilly, received the award for "Services to Nautical Archaeology and Maritime Heritage".
He said he was delighted - but was quick to credit others.
"I couldn't do all that I have done without having worked with so many wonderful diving teams and other people," he told Divernet, "particularly in relation to protected wrecks.
"I owe a lot of people, including Bridget, my wife of 35 years, a great debt of gratitude."
Larn's candidacy for an OBE was backed by Margaret Rule, the archaeologist who directed excavation of the Mary Rose; Barbara Jones, Corporate Information Officer at Lloyds Register of Shipping; David Clement, President of the South West Maritime History Society; and Alan Aberg, formerly of the Royal Commission for Historic Monuments (which became English Heritage).
Larn's achievements include the creation of the Shipwreck Index of the British Isles and the Shipwreck Index of Ireland, the result of a decade's work. Resources for the project were developed through Shipwrecks UK Ltd, of which Larn is Chairman and his wife is a director.
For more on Richard Larn’s broad-ranging achievements, go to his company's website, www.shipwrecks.uk.com