Whiteside grows up on Shankill Road, and because of his aggressive, physical playing style he is later nicknamed the “Shankill Skinhead” by Manchester United supporters. The family later moves to 10 Danube Street. He remains relatively unscathed by The Troubles as his Protestant parents keep a firm watch on their children to ensure that they do not stray far from home and that none of them become involved with Ulster loyalism. At around seven years of age he joins the Boys’ Brigade, and quickly shows his natural talent for football, scoring ten goals in a game against boys almost twice his age. He is educated at Cairnmartin High School, and becomes famous in the Shankill area as a footballing prodigy by the age of eleven.
Whiteside is said to have been discovered by Ipswich Town scout Jim Rodgers, who is told by manager Bobby Robson to wait until Whiteside grows older. Instead, it is Manchester United’s 80-year-old Ulster scout Bob Bishop, who previously unearthed Belfast-born George Best and Sammy McIlroy for the club, who first offers him a trial at an English club. He finds that he has been offered schoolboy terms at the club during a school trip to the United States, on which he and his classmates meet President Jimmy Carter in the Oval Office, a rare and extraordinary occasion for children from a disadvantaged background.
Whiteside signs professional forms in 1982 at the age of 17 and quickly becomes a key member of the Manchester United club. He scores 68 goals in 278 league and cup appearances for the club over the next seven years, picking up two FA Cup winners medals in 1983 and 1985, as well as playing in the 1982 FA Youth Cup final, the 1983 League Cup final, and the FA Charity Shield in 1983.
Whiteside remains with United until July 1989, when he is sold to Everton F.C. for £600,000. However intense running sessions run by coach Mick Lyons take their toll on his right knee, and on September 20, 1990 he takes a knock in a practice match, which requires him to have another operation on his right knee. After the return of Howard Kendall as manager in November 1990, he manages to appear in a few reserve team games, but this only delays the inevitable, and he is forced to retire from the game at the age of 26 in June 1991.
Upon retirement, Whiteside studies to become a podiatrist, graduating with a degree from the University of Salford, and serves Northwich Victoria F.C. as their assistant manager/physio from October 1991 until March 1992. He quits the role as he does not enjoy the amount of time spent travelling between games. He instead became an after-dinner speaker and also works for the Professional Footballers’ Association, while taking a postgraduate course at Manchester Metropolitan University. He later takes up private practice as a podiatrist in Manchester. Since 1994, he has also worked at the corporate hospitality department at Old Trafford. In 2003, he releases a book entitled My Memories of Manchester United. With the help of writer Rob Bagchi, he releases his autobiography entitled Determined in August 2007, published by Headline Publishing Group, and with a foreword by actor James Nesbitt.
Whiteside holds records as the youngest player to take part in a World Cup, the youngest player to score in a League Cup and FA Cup final, and the youngest player to score a senior goal for Manchester United. Winning 38 caps for Northern Ireland, he plays at the 1982 and 1986 World Cups, and also helps his country to win the last ever British Home Championship in 1983–1984.