White was born in Baltimore, Maryland, on September 27, 1921. His official biography reported that he "ran away to join the circus" as a child. White was born near the old Royal Theatre in Baltimore, where by the age of 10, he used to dance outside for coins and sold candy at the theater. He left Baltimore at the age of 13 because he was in danger of being sent to reform school because of his school absences. White joined a traveling carnival and made a living as a tap Dancer with the troupe. He was eventually picked up by police and returned to his family, but could not trade show Business for school. He received his nickname from the manager of a local theater where he entered a talent contest with a friend; the manager billed them as "Slap and Happy".

He began his career as a Dancer and did not turn to comedy until 1940 when he joined with a fellow hoofer and labeled his act the "Two Zephyrs". White and his partner, Clarence Schelle, had appeared on The Major Bowes Amateur Hour. The "Two Zephyrs" made the circuits together for over four years appearing with such notables as Lionel Hampton, Count Basie, Duke Ellington and many others. With his team "Slappy" was first introduced to Californians, making his West Coast debut in Los Angeles at the Orpheum Theatre along with Louis Armstrong.

The team with which he is best known is "Redd Foxx and 'Slappy' White". Foxx and White met in Harlem in 1947 and formed a comedy team. They toured from coast to coast with the Billy Eckstine Orchestra for more than four years. Some years before, White had met and married Pearl Bailey, when both of them were still relatively unknown professionally. Bailey's career was on the way up. She was performing in the better nightclubs with people like Duke Ellington and Cab Calloway while White was still struggling in lesser venues. The marriage was in trouble at the time White and Foxx first met. The couple divorced. Years later, when White and Dancer Bill Bailey, who was Pearl's brother, teamed up for an act, White joked that the act would be billed as "Rev. Bill Bailey and his ex-brother-in-law".

White was a performer in Las Vegas for many years. In the 1950s while he was on the bill with Dinah Washington, White performed his routine which made the nightclub's manager the target of his jokes. While there was nothing offensive about the jokes White told, there was an unwritten rule about black comedians targeting whites in this manner. The manager fired White, but changed his mind about the comedian's employment when Dinah Washington indicated she would withdraw her entire act because of White's firing. White spent four years with Dinah Washington before establishing himself as a solo act.

"Slappy's" solo career started in 1951 when Dinah Washington requested him to introduce her act at the Black Hawk in San Francisco. White started out as a chauffeur to the singer, entertaining her with jokes as he drove. When she was late arriving on stage one evening, Washington, worried about the waiting audience, asked White to go on stage and "say something funny" while she prepared for her performance. "Slappy" was such a hit with the patrons, she kept him on as her opening act. He was once also married to Rock and Roll Hall of Fame inductee and blues belter, LaVern Baker (1929-1997).

White wrote and performed a comedy routine called "Brotherhood Creed" using one black and one white glove while reciting his poem about equality between men. White performed the routine many times during the civil rights movement in America, and President John F. Kennedy once gave it a personal commendation. In 1965, White was invited to perform the "Brotherhood Creed" before the Massachusetts State Senate. He was also well known as a Comedian who eschewed offensive material in his nightclub act.

In 1969, he formed a new comedy team called Rossi and White with Steve Rossi, who formerly worked with Marty Allen. The pair entertained at the White House in May of the same year. Rossi and White also performed their act aboard a National Overseas Airlines FLIGHT from Chicago to Spain. The airline had hoped that providing live entertainment on their flights would boost ticket sales.

Later in life, he performed under his given name on his friend Redd Foxx's TV show Sanford and Son as Fred's friend, also named Melvin, and had a million dollar contract to perform at the Flamingo Hotel in Las Vegas in 1973.

In 1986 Milton Berle planned to introduce a new situation comedy called Moscow & Vine, with White as his co-star on the show. White's role was to be that of Berle's old vaudeville partner and as an employee in the music store owned by Berle's character. At one time, Berle hoped to syndicate the program.