The relaunched service was to have sailed again on St David's Day
A reinstated ferry service between Swansea and Cork is making its first sailing.
The ferry has set sail from Swansea after completing certification and safety checks and will arrive in Ireland at 0750 GMT on Thursday.
The Julia will then depart Cork for Swansea on Thursday night.
The service was due to restart on 1 March but crossings were cancelled as it awaited checks by UK government maritime authorities.
Owners Fastnet Line said the ferry had now completed certification and safety checks, and "met the strict requirements demanded by the International Safety Management Code".
Chief executive Tom Barrett said: "We have an excellent team aboard the ship, are very confident that the route will succeed and are heartened by the support from both sides of the Irish Sea to date."
The last time the service ran was in 2006. There was a plan to restart the service in 2009 but it was abandoned.
The Julia, which can carry more than 1,800 passengers and 400 cars, had already received her Passenger Ship Safety Certificate.
The ferry was previously sailing in the Baltic Sea and was bought by a co-operative for £6.9m last year.