Situated on the shores of Narragansett Bay, near Newport in Rhode Island, Portsmouth Abbey was founded on 18th October, 1918 by the Bostonian, Dom Leonard Sargent. A convert from the Episcopalian Church he had become a monk of Downside in 1915. On 25th June, 1919 the priory was formally inaugurated under the jurisdiction of Downside Abbey. In 1926, this jurisdiction was transferred to Fort Augustus Abbey, and the nucleus of a school was started under the headmastership of Dom Hugh Diman.

At the outbreak of the 2nd World War the novitiate was transferred from Fort Augustus to St Anselm’s, Washington, where it remained until Portsmouth became an independent priory, on 21st November, 1949 - 30 years to the day after the first two monks, Dom Leonard Sargent and Dom Benedict Brosnahan had taken up residence.

In 1956, work commenced on the building of the new priory church which was opened in 1960, along with the new monastery building. In 1969, the priory was raised to the status of an abbey.