The life of the REX ocean liner began on 27 April 1930 at the Ansaldo shipyard in Sestri Ponente, in Genoa, Italy, with the ceremony of the first hull sheet. It was built in only fifteen months and was launched on 1 August 1931; an event that was presided by King Vittorio Emanuele III, and Queen Elena of Montenegro as godmother, in the presence of about 200,000 people.

It left Genoa for its first trip on 27 September 1932, in the presence of 15,000 people, for the transatlantic service between Genoa, Naples, Villafranca-Cannes, Gibraltar, and New York. On first arriving in New York, it was welcomed triumphantly and visited by over 50,000 people.