The Christian Brothers were founded in 1802 by a Waterford widower called Edmund Ignatius Rice, who had given up his merchant business after his wife's death and devoted the rest of his life to educating Ireland's Catholic poor. The order's original mission was simple literacy for boys who had no other access to schooling. By 1856 the model had expanded enough to support the new school in Kingstown, financed by what the early records describe as 'voluntary subscriptions, solicited and collected by the Brothers' - a delicate phrase for door-to-door fundraising in a country still recovering from famine. The first superior was Brother Alphonsus Hoope. There were six brothers living on the school grounds in a small house behind the main building. The first students were the children of dock workers, shopkeepers, and labourers in a port town being rapidly transformed by the new piers and the Dublin and Kingstown Railway, the first railway in Ireland, which had opened in 1834.

The decision to play rugby rather than Gaelic football marked CBC Monkstown out from almost every other Christian Brothers school in the country. The order's broader ethos in the early twentieth century was strongly nationalist and Gaelic: CBS schools, as they were generally known, played hurling and Gaelic football. Monkstown went the other way. Its sister institution, CBC Cork - usually called Christians - had taken the same decision a few decades earlier, and the two formed a small Christian Brothers rugby subculture within an order that otherwise wanted nothing to do with the game. CBC Monkstown won the Leinster Schools Rugby Senior Cup in 1976 and reached the final again in 1984; the school played in the Senior League final in 2001, 2003, and 2008, winning the last. The Senior Cup team has won the Vinnie Murray Cup four times. The 2008 group of senior players were named Leinster Rugby School of the Year. The school has produced Irish international rugby players including Patrick Casey and Paddy O'Donoghue, plus the international referee Donal Courtney and John Lyons, a past president of the IRFU.

In 1958, CBC Monkstown became the first school of any kind to perform on the stage of Ireland's national theatre. Class V at the college mounted a production of Patrick Pearse's Irish-language one-act play Iosagan, directed by the school's drama and elocution teacher Thomas MacAnna - the same MacAnna who would later win a Tony Award as an Abbey Theatre director. MacAnna also produced the school's early Gilbert and Sullivan operas. The drama tradition has continued through annual musicals with the nearby Loreto College Foxrock and through a strong debating culture: CBC was the first school in the history of the Leinster Schools' Debating Championships to win both the Individual and Team prizes in the same year (2011), and in 2023 a CBC student became the first Irish student to win both the Oxford Union and the Cambridge Union schools debating competitions, the two largest schools debating contests in the world. In 2015 Roddy Doyle edited a short-story collection by the Transition Year class, Brainstorms, with an introduction by Kevin Barry.

The college occupies the grounds of a country house called Monkstown Park, built in 1843 for the antiquarian and merchant Charles Haliday. Haliday's house is still incorporated into the main school block, its long Corinthian portico intact as a protected structure. A separate tower on the grounds, also from Haliday's time, is also protected - one of the small group of survivors of the Georgian and early-Victorian villas that once dotted this stretch of coast. Carrickbrennan churchyard, dating to medieval Monkstown, borders the school to the north. Monkstown Castle, a fourteenth-century Cistercian house belonging in its time to St Mary's Abbey in Dublin, is adjacent. The school's playing fields - three rugby pitches and an athletics paddock - occupy ground that was the country estate of one of Dun Laoghaire's wealthier nineteenth-century families. The Brothers bought it in 1949 from the Protestant Corrig School, swapping their existing playing fields at Rochestown Avenue to Dun Laoghaire Corporation in exchange. Most of the surrounding parkland is now suburban housing; what survives at Monkstown Park is a green island in a sea of semi-detached homes.

The school's alumni list is unusually weighted towards arts and entertainment for a Christian Brothers school. Ronnie Drew, the gravel-voiced co-founder of the Dubliners folk group, was a pupil. So was Dan O'Herlihy, the actor who earned an Academy Award nomination for Robinson Crusoe in 1954. James Flynn and Jonathan Redmond, both Oscar nominees in more recent years - Flynn for the short film The Door, Redmond for editing Elvis - are alumni. The drummer Robbie Brennan played with Thin Lizzy. The playwright Bernard Farrell, whose stage comedies have been Abbey staples for decades, attended. Sean Barrett, Ceann Comhairle of the Dail and former cabinet minister, was a pupil. So was Tim Pat Coogan, the historian who edited the Irish Press for thirty years. John O'Shea, who founded the international development charity GOAL in 1977, attended. Father Shay Cullen, founder of the Preda Foundation that has rescued thousands of trafficked children in the Philippines, is an alumnus. The school motto - Certa Bonum Certamen, fight the good fight - has been applied across a wider range of fights than its founders might have predicted.