Purcell was elected to the Eighty-seventh Congress, by special election, to fill the vacancy caused by the resignation of fellow Democrat, Representative Frank N. Ikard. He was reelected to the five succeeding congresses (January 27, 1962 – January 3, 1973). In 1966, when John Tower won his second term as U. S. senator, Purcell defeated the Republican Dillard Carlisle "Bunny" Norwood (1913-1993) of Wichita Falls.
On November 22, 1963, Purcell was riding in the motorcade's third vehicle behind U.S. President Kennedy during the assassination in Dallas, Texas.
Although Texas gained a seat as a result of the 1970 Census, Purcell's 13th District was dismantled, and his home in Wichita Falls was merged with the Panhandle-based 18th District of Republican Bob Price for the 1972 elections. The new district was numerically Purcell's district—the 13th—but was geographically more Price's district. Purcell retained only one-third of his former constituents. Forced to run in territory that he did not know and that did not know him, Purcell was defeated by nine points.
In 1993, House bill HR 2292 was passed designating the federal building in Wichita Falls as the Graham B. Purcell Jr. Post Office and Federal Building.[2] Purcell resided in Wichita Falls until his death at the age of ninety-two.