The six-time world champion rower, now a TV presenter, will open the Titanic-themed attraction 100 years to the day after the ship left the city on its doomed maiden voyage.
The opening of the museum is the centrepiece of Southampton's commemorations to mark the centenary of the world's most infamous shipping disaster.
James said: “This is a very special time for the city of Southampton and I'm honoured to be part of such an important event."
The former rower, who received the OBE in 2004 for his services to sport, will be joined in performing the opening by two Southampton schoolchildren whose great-grandfather survived the 1912 tragedy, which claimed the lives of more than 1,500 people, including more than 500 city residents.
Eight and six year-olds Henry and William Ward, who attend Bitterne Park junior and infant schools, will take part in the April 10 ceremony as descendents of Shirley-based George Kemish, who was a fireman on Titanic.
More than 600 city school pupils will feature in the official opening, taking part in a procession and each holding a placard dedicated to a Southampton crew member who sailed on the ship, famously dubbed “unsinkable” before its one and only voyage.