The origins of the Old Thomians Association date back to 1953, when a group of former students of Mr. Charles Robinson founded the Old Boys' Association (OBA) with his support, as Mr. K M D Jayanetti as the founder President. Initially, this was the sole organization for alumni. However, the introduction of the Swabhasha medium of instruction created a divide. As a result, both groups adopted a "live and let live" approach.

In the early 1970s, Mr. Asoka Deegahawathura, a former student of Mr. A.J. Wijesinghe, attempted to revive the OBA. Despite his efforts, this revival was short-lived, and the college lacked an active Old Boys' Association for some time.

In 1983, another group of former students successfully revitalized the OBA with the backing of then-principal Mr. Wijesinghe. They forged a strong, enduring relationship with the school authorities, driven by a clear vision and steadfast discipline.

This initiative has been highly successful, leading to the current prominence of St. Thomas' College Matale. Today, the institution boasts four local branches and three overseas branches, in addition to the main body in Matale.

For the past four decades, the Mother Association has been a vibrant presence in Matale, continually keeping the ball rolling. They have organized numerous events, including an Old Thomians’ Sports Festival, a Back to School program, and a felicitation ceremony for the distinguished Old Thomian, General Shavendra Silva, the Chief of Staff and the 23rd Commander of the Sri Lanka Army.

The Association has been actively involved in supporting the college during the annual inter-house sports meet, Colours Nite, and prize-giving events. Their colorful annual general meetings always attract a large number of old Thomians.

In addition to these activities, the Mother in various social projects in Matale and collaborates closely with all other Old Boys' Associations of STC Matale currently operating in Sri Lanka.

The Mother Association has successfully established a dedicated office within the school premises, fulfilling a long-standing need through successful negotiations with the school administration.

A recent initiative to enroll young Thomians who have graduated is proving timely and beneficial, paying significant dividends.