Dedicated on December 2, 1911, Lower Merion Senior High School was an impressive granite and stone edifice considered one of the finest new educational facilities in the state.

The 17-acre (69,000 m2) property, complete with three stone-arch entrances, landscaped grounds, and a football stadium, eventually grew to 23 acres (93,000 m2) with the purchase and annexation of the Clarke House.

In 1950, a cafeteria/library wing, designed by the Philadelphia firm of Savory, Scheetz and Gilmour, was added near Pennypacker athletic field.

That same year the 18-acre (73,000 m2) General Henry Harley "Hap" Arnold athletic fields opened directly across Montgomery Ave. By 1957, enrollment had grown to 1,663 students and the time had come to build a second high school (Harriton) in Lower Merion Township.

Rooms in the technical building were converted to other uses, including art classes, computer labs, and the school's television studio.

Demolition of the "Ardmore Annex", the natatorium, and one of the school's two gyms commenced in the summer of 2008 to make way for construction.

In addition to state-of-the-art classrooms, science laboratories, art classrooms, and music rehearsal spaces, the new Lower Merion features a lecture hall with tiered seating, a multi-purpose black box theater, an 850-seat auditorium/theater, a greenhouse for environmental and horticultural studies, high-performance athletic facilities, a swimming pool, a television studio, multi-media production facilities, a music technology lab, an expansive courtyard, and a two-story, glass-encased library that serves as the building's exterior focal point along Montgomery Avenue.

The new school was constructed adjacent to the historic district administration office (DAO) building, which is the only original structure that remains on the site.

On November 13, 2021, the school principal, Sean Hughes, was killed in a car crash while driving his teenage son to a soccer game.

Fall sports include cheerleading, cross country, field hockey, football, golf, soccer, tennis, volleyball, and water polo.

Winter sports include basketball, ice hockey, indoor track, squash, swimming, and wrestling.

Spring sports include baseball, crew, lacrosse, softball, tennis, track and field, ultimate frisbee, and volleyball.

[3] The Lower Merion High School basketball team has won seven Pennsylvania Interscholastic Athletic Association State Championships.

[9] The Lower Merion boys' varsity Lacrosse team has won seven PIAA and or Pennsylvania Scholastic State Championships, (1966, 1967, 1969, 1977, 1979, 1984, 1999) the most of any high school in the Commonwealth, came in second three times (1970, 1978, and 1980)[10] and have had 21 players be named All-American.

The Federal Bureau of Investigation (FBI), U.S. Attorney's Office, and Montgomery County School District attorney all initiated criminal investigations of the matter, which they combined and then closed because they did not find evidence "that would establish beyond a reasonable doubt that anyone involved had criminal intent".