Under the leadership of the then principal Sister Immaculata O'Connor, the Friends of St. Mary's was formed with the purpose of raising funds to finance the building programme.

In 2003, the school trustees completed a further phase of the development programme when Cafe Bordeaux and a new classroom extension were opened.

St. Mary's Grammar School has over eleven hundred pupils on roll, with an equal ratio of boys and girls and serves three counties: Londonderry, Antrim and Tyrone.

[citation needed] September 2004 marked another beginning in the school's history with the appointment of its first male Principal, Mr D A Lambon.

[2] In 2018 it was ranked joint 1st for its GCSE performance with 100% of its entrants receiving five or more GCSEs at grades A* to C, including the core subjects English and Maths.

St Ronan's will go on to represent Ulster in the Hogan Cup against the other respective provincial schools winners.

They meet at lunch time each week, and activities include quizzes, bingo, and teaching students how to make St Brigid's Crosses (Crosóg Bríghde).

Student who excel in the various activities get to win prizes which are always linked to the Irish Language, such as Gael Linn or Foras na Gaeilge merchandise.