LÉ Niamh was built in Appledore Shipyards in the UK for the Naval Service. She is an improved version of her sister ship, LÉ Róisín and Naval Service engineers stood by her construction at all stages. She is built to the successful Róisín design that optimizes her patrol performance in Irish waters (which are among the roughest in the world), year round. For that reason a greater length overall (78.8m) was chosen, giving her a long, sleek appearance.

Following the dictum that sailors at sea should be provided with as much comfort and dignity as the harsh environment allows, the facilities onboard include more private accommodation, a gymnasium and changing areas and storage areas.

Her main armament is a 76mm OTO MELARA compact gun and RADAMEC fire control system which is tied in to the integrated bridge system. She also has a highly automated engine room. Her twin WARTSILA diesels give her efficient patrolling ability with good speed performance when required.

One of Niamh most notable episodes was her trip to Asia in 2002, which was the first ever visit by an Irish warship to that part of the world and included official visits to China, Japan, Korea and Malaysia, together with a refueling stop in India and a UN resupply visit to Irish troops based in Eritrea.