Liam Sullivan's educational journey began at Illinois College, where he concurrently explored his early passion for acting in regional theater. He later pursued a drama degree at Harvard University, before making his way to New York City to debut on Broadway in the 1951 production of "The Constant Nymph". Returning to the West Coast, Sullivan took to the stage once more, this time in an LA production of "Mary Stuart".
As the 1950s progressed, Sullivan began to make a name for himself in television, leveraging his striking Romanesque features and refined voice to portray a range of characters, from the suave and sophisticated to the arrogant and cynical. His versatility allowed him to seamlessly transition between genres, including westerns and science fiction.
Among his numerous television credits, two performances stand out in particular. In the 1966 episode of "Star Trek" titled "Plato's Stepchildren", Sullivan brought to life the complex and intriguing character of Parmen, a philosopher-king with a penchant for manipulation. In another notable appearance, Sullivan played Jamie Tennyson, a social-climbing upstart who makes a bet with disastrous consequences in the 1959 episode of "The Twilight Zone" titled "The Silence". This episode, based on a short story by Anton Chekhov, saw Sullivan's character attempt to remain silent for a year, with devastating consequences.
Sullivan also appeared in another "Twilight Zone" episode, "The Changing of the Guard", although his performance was somewhat overshadowed by the poignant portrayal delivered by Donald Pleasence.
In the latter stages of his life, Sullivan combined his acting career with writing pursuits, working on a novel just prior to his passing. Additionally, he was in the process of compiling a biographical history of the Eli Bridge Company, a family-owned business founded by his ancestor W.E. Sullivan in 1900. Despite his passing, the company remains family-run to this day, a testament to Sullivan's enduring legacy.