Mister Softee, Inc., was founded in 1956 in Philadelphia by two Philadelphia-born brothers, William Conway (né William Aloysius Conway; 1922–2004) and James Conway (né James Francis Conway; 1927–2006). Another brother, Joseph Patrick Conway (1926–1961), joined the firm and in 1961 moved to Illinois to serve as President of Mister Softee of Illinois, Inc., but died a month later in an auto accident in Chicago at age 35. A fourth brother, the oldest, Monsignor Walter Joseph Conway (1921–2000), was a clergyman with the Roman Catholic Archdiocese of Philadelphia. Their only other sibling, John Conway (1924–1933), died at age 9.
Mister Softee became one of the largest franchisors of soft ice cream in the United States, with about 350 franchisees operating 600 trucks in 15 states. Since 1959, and as of 2016, Mister Softee, Inc., has been headquartered in Runnemede, New Jersey, and is still owned and operated by members of the Conway family. Around 1999, William and James' sons, John P. Conway (born 1953) and Jim Conway, Jr. (born 1956), took over the business.