Founded in the spring of 1823 as Washington College under the leadership of Episcopal Bishop Thomas C. Brownell, the school was established as an alternative to the Congregational-dominated Yale College and was the second college in the state. Although its founder was the Bishop of the Episcopal Diocese of Connecticut, the college charter prohibited the imposition of religious standards on any student or faculty member.

The first campus consisted of two Greek Revival-style buildings – Seabury Hall and Jarvis Hall. Both made of Portland brownstone, the latter building was designed by Samuel Willard, the architect of the Bunker Hill Monument. The school was situated atop "College Hill," where the state capitol now stands overlooking what has become Bushnell Park.

At the annual meeting of alumni in 1844, a proposal was made to rename the school from Washington College to Trinity College, partly due to the prestige of the name associated with the college in England.

In 1871, the city of Hartford wished to offer the "College Hill" property to the State of Connecticut in order to construct a new capitol building. College trustees twice rejected the city's offer but, in 1872, voted to sell the property to the city in consideration of $600,000, with the provision that the school be allowed to use the buildings for the next five years.

The following year, a parcel of 80 acres was purchased on another hill in Hartford – one that had been known as "Gallows Hill" due to the public executions held there. The site commanded magnificent views of the surrounding area. Plans were drawn up to design a campus comprised of brownstone, Gothic-style college buildings in four quadrangles.

Those plans were never entirely fulfilled. Although Trinity College is still situated at the site to which it relocated, only one of the quads was ever built. The buildings that surround the main quad are an early example of “collegiate Gothic” architecture in America. By the mid-19th century, the area became known as Zion Hill.

An all-male school from its beginnings, Trinity College began admitting women as undergraduates in the late 1960's.

In 1995, Trinity turned its attention to the needs of the neighborhoods surrounding its campus. The "Learning Corridor," was constructed, comprised of a public, Montessori-style elementary school, neighborhood middle school, math, science and art high school resource center to serve suburban as well as Hartford students and teachers, center for families and child care, the first Boys & Girls Club in the country to be located at a college, and a health and technology center. These resources provide Trinity students and faculty with opportunities to engage in volunteer work, internships and research projects.

In addition, Trinity has developed the Hartford Studies Project, which maintains an archive documenting the city’s history since the 1880s, organizes public events such as exhibits and fora, and sponsors "The History of Hartford," a twice-annual course offered to undergraduate and grad students.