OLMC was first established in the 1930s on the Esplanade at Cronulla and was located there until 1960.
The current property at Burraneer was purchased from Mr Charles Duncan who lived there for a number of years before leasing it to the Cronulla Country Club.
The College was officially opened and blessed on Sunday October 16, 1960 by His Eminence N.T. Gilroy, Archbishop of Sydney. The total number of students enrolled was 199 with 7 staff and Sister M. Alphonsus the Principal.
In 1966 the Catholic Education Office established Our Lady of Mercy College as a Regional School and enrolments increased to 439. Temporary buildings were erected in 1967 on the bowling greens and the Science Block was completed. Principals during this period included Sr. M. Anne Ryan, Sr. M. Paulinus and Sr. Immaculata Hegarty.
The old Art cottage was purchased in 1974 and the Library and classroom extensions were officially opened by Cardinal Freeman and the Hon. E. G. Whitlam, then Prime Minister. In 1976 the old Music room was built. Principals of this decade included Sr. Pauline N. Smith and Sr. Margaret Doyle.
In 1982 the Sisters of Mercy Community moved out of the the Convent and in 1984 allowed the school to extend into this part of the building. Renovations and refurbishments including verandahs and staircases to link the buildings were completed in 1988.
Building projects continued in this decade which saw adjacent land purchased to house a new Art demountable, linking of the two existing buildings, resurfacing of the basketball court, extensions and development of a Home Science (TAS) area. The new extensions were blessed and opened by Bishop David Cremin.
In 1989, after extensive community consultation, a new uniform was introduced replacing the traditional yellow and brown. With the uniform change came the new school colours of red, white and blue.
The Art rooms moved back across to the main site and demountables across the road were removed. Extensive building work was completed in late 2003 and the College now has a multi-purpose hall, new music and practice rooms, and 5 new general classrooms.