Lomond School was formed in 1977 as the result of a merger between Larchfield Boys' Preparatory School which dated back to 1845, and St Bride’s Girls’ School, which was founded (as Helensburgh High School) in 1895. These two schools were a few hundred yards apart in the west end of Helensburgh, so initially Lomond operated on a split site.
After a major fire in 1997, the old St Bride’s building was largely destroyed and a modern replacement was constructed on the same site. Fortunately the 1902 hall and the 1923 library survived the fire.
Boarding was always an important element of Larchfield and St Bride’s, and today up to 60 male and female boarders are housed at Burnbrae, which was constructed in 2003 on the site of the former boys’ boarding house which bore the same name. The international element at Burnbrae is an important feature of the school.