Witherspoon had eight amateur bouts, losing one to Marvis Frazier on decision after getting knocked down.
Making his professional debut with a first-round TKO over Joe Adams on October 30, 1979, Witherspoon quickly rose through the ranks. In 1981 he participated in his first high profile fight, knocking out future Cruiserweight world champion Alfonzo Ratliff, after which he was signed by an impressed Don King. Witherspoon was a sparring partner of Ali as he was training to fight Larry Holmes and Trevor Berbick.
In 1982 he was matched with Renaldo Snipes, who had just given champion Larry Holmes a stiff challenge (and knocked Holmes down), and outpointed him over 10 rounds, setting up his own challenge to Holmes.
On May 20, 1983, Witherspoon would have his first attempt at earning a world title by taking on the recognized top man in the division World Boxing Council champion Larry Holmes at the Dunes Hotel in Las Vegas. Witherspoon, a relative unknown, utilized his awkward style and natural physical strength and fought valiantly. However, he was judged to have been defeateded by a split decision. Years later Boxing Monthly would cite this decision as one of the 10 most controversial in history.
However Witherspoon had caused a stir with his showing and the expectations of a potentially glorious career would color what he eventually did accomplish. He returned later in the year to outpoint Floyd "Jumbo" Cummings, who had drawn with Joe Frazier in Smokin Joe's last fight, and win the NABF title impressively with a first round knockout of James "Quick" Tillis.
Witherspoon's second reign as a Heavyweight champion saw him travel to London, England and defend his title against hard hitting local Frank Bruno in front of 60,000 fans. After a tough, bruising fight, Witherspoon came from behind to stop Bruno in the 11th, retaining his title. After the fight, Bruno would receive a million sterling from his promoters. Witherspoon, due the same amount, devastatingly received less than $100,000 after Don King's creative accounting and deductions.
Witherspoon was matched with ex-victim James 'Bonecrusher' Smith in December 1986, after Tony Tubbs opted out of a rematch at the last minute. Knowing of Witherspoon's turmoil, Smith wisely came out fast and crushed Witherspoon in the opening round, knocking him down three times.
In 1993 Don King settled out of court and paid Witherspoon a million dollars. By 1994 a new and in shape Witherspoon was back, winning five fights in a row by knockout. Aged 38 he was inked by HBO and matched in high profile fights with Cruiserweight champion Al Cole and the Cuban amateur legend Jorge Luis Gonzales, both of whom he defeated comprehensively. Later in the year he was matched with Ray Mercer but lost a highly controversial decision.
After that loss Witherspoon laid off a year, and when he came back he had lost his edge. The ageing, out-of-shape fighter was outpointed convincingly by the slick Larry Donald on HBO, and, in 1998, lost a close decision when outworked by New Zealand muscleman Jimmy Thunder before travelling to Poland to be outpointed by Andrew Golota.
Surprisingly, a 43 year old Witherspoon resurfaced in 2001, knocking out the usually durable prospect David Bostice in one round, outpointing Cuban southpaw contender Eliecer Castillo and huge Syrian Ahmed Abdin, before his revival was ended by hard hitting white heavyweight Lou Savarese who stopped him in five rounds.
Witherspoon also competed in Cedric Kushner's 2003 Thunderbox Heavyweight Tournament, "Fistful of Dollars," but at 45 looked his age and lost in the opening stages.
Tim now resides in an area around Philadelphia, Pennsylvania, where he trains boxers, including his son, lightweight Tim Witherspoon Jr.; a heavyweight prospect named Robert Atkins; and many others. He has also trained Light Heavyweight champion Clinton Woods in the U.K.
Instead of going to trial, King agreed to settle the case for $1 million.