The school’s primary language of instruction is English, and it also offers the International Baccalaureate program.

The school was founded in 1954 by the Brothers of Christian Instruction and resides in the St. Francis Xavier district of the FIC.

St. Mary's offers religious instruction, and Catholic students may attend mass.

[5][6] The 9-acre (36,000 m2) campus features a large, lighted indoor swimming pool with a balcony for visiting audiences, an indoor multi-athletic court with a contractable stage + seats, a large multi purpose hall which converts into an auditorium, number of tennis courts, two outdoor basketball courts, a large soccer field with appropriate synthetic grass, a mass of gardened land, and numbers of other athletic facilities.

These award-winning choirs have performed in the United States, Austria, Hungary, Canada, Australia, China, South Korea, Indonesia, and many other countries.

St. Mary's high schoolers may also take part in the Tokyo Area Honor Choir amongst other KPASSP schools, if they are accepted through auditioning.

Similarly to the choir, high schoolers may take part in the Tokyo Area Honor Band amongst other KPASSP schools, if they are accepted through auditioning.

The team has won the annual Kanto Plains Debate Tournament three years in a row, from 2010 to 2012.

In the most recent tournament, held at Seisen in Fall 2012, the SMIS Speech Team won second place.

The main academic and administrative center has opened on the site of the former sports field, in March 2009.