Watching and playing sports is an important part of Belfast culture. Almost six out of ten (59%) of the adult population in Northern Ireland regularly participate in one or more sports. Belfast has several notable sports teams playing a diverse variety of sports including association football, rugby, Gaelic games, and ice hockey. The Belfast Marathon is run annually on May Day, and attracted 14,300 participants in 2007. The Northern Ireland national football team, ranked 27th in September 2007 in the FIFA World Rankings, and 1st in the FIFA rankings per capita in April 2007 plays its home matches in Windsor Park. The 2007-08 Irish League champions Linfield are also based at Windsor Park, in the south of the city. Other teams include Glentoran based in east Belfast, Cliftonville and Crusaders in north Belfast and Donegal Celtic in west Belfast. Belfast was the home town of the renowned player George Best who died in November 2005. On the day he was buried in the city, 100,000 people lined the route from his home on the Cregagh Road to Roselawn cemetery. Since his death the City Airport was named after him and a trust has been set up to fund a memorial to him in the city centre.

Gaelic football is the most popular spectator sport in Ireland, and Belfast is home to over twenty football and hurling clubs. Casement Park in West Belfast, home to the Antrim county teams, has a capacity of 32,000 which makes it the second largest Gaelic Athletic Association ground in Ulster. The 2006 Celtic League champions and 1999 European Rugby Union champions Ulster play at Ravenhill in South Belfast. Belfast has four teams in rugby's All-Ireland League: Belfast Harlequins (who play at Deramore Park in south Belfast) and Malone (who play at Gibson Park in south-east Belfast) are in the Second Division; and Instonians (Shaw's Bridge, south Belfast) and Queen's University RFC (south Belfast) are in the Third Division.

Belfast boasts Ireland's premier cricket venue at Stormont. The Ireland cricket team plays many of its home games at this venue, which in 2006 hosted the first ever One Day International between Ireland and England. In 2007, Ireland, India and South Africa played a triangular series of one-day internationals at Stormont, and in 2008 the qualifying tournament for the ICC World Twenty20 was held there. At club level, Belfast has seven senior teams: Instonians (Shaw's Bridge, south Belfast) and Civil Service North (Stormont, east Belfast) are in Section 1 of the Northern Cricket Union League; CIYMS (Circular Road, east Belfast), Cooke Collegians (Shaw's Bridge) and Woodvale (Ballygomartin Road, west Belfast) are in Section 2; and Cregagh (Gibson Park, south-east Belfast) and Police Service of Northern Ireland (Newforge Lane, south Belfast) are in Section 4.

Ireland's first professional ice hockey team, the Belfast Giants play their home matches at the Odyssey Arena, watched by up to seven thousand fans. The Belfast Bulls and Belfast Trojans American football teams represent Belfast in the IAFL, competing for the Shamrock Bowl. Other significant sportspeople from Belfast include double world snooker champion Alex "Hurricane" Higgins and world champion boxers Wayne McCullough and Rinty Monaghan.