The palace was conceived as a great public venue for north London — an equivalent to Crystal Palace in the south — designed to welcome everyone. The original plan called for a glass structure; what was built instead was a more conventional Victorian pile by architects John Johnson and Alfred Meeson, using recycled construction materials from the 1862 International Exhibition building in South Kensington. By 1900, the private owners were planning to sell the site for redevelopment. A consortium led by Henry Burt, a member of Middlesex County Council, raised the money to buy it. An Act of Parliament created the Alexandra Palace and Park Trust, with a legally binding requirement to keep both building and park available for the free use and recreation of the public — forever. The present trustee is the London Borough of Haringey, whose coat of arms features lightning bolts referencing the building's later role in television history.

During the First World War, Alexandra Palace served first as a refugee camp for displaced Belgians, then from 1915 to 1919 as an internment camp for German and Austrian civilians. The Henry Willis organ installed in 1875 — declared by organist Marcel Dupré to be the finest concert organ in Europe in its restored form — was vandalised in 1918 and not restored until 1929. In 1944 a German V-1 flying bomb exploded outside the organ end of the Great Hall, blowing in the Rose Window and exposing the instrument to the elements. The rose window was repaired in 1947 using the shattered fragments incorporated into a new design. Then, in 1980, a fire during Capital Radio's Jazz Festival destroyed half the building. The outer walls survived again. The organ was partly saved because it had been dismantled for repairs — most of the pipework was off-site. The same basic structure that had survived 1873 survived again.

In 1935 the BBC leased the eastern section of the palace to establish a production and transmission centre for their new television service. On 2 November 1936, Alexandra Palace became the site of the world's first regular public high-definition television broadcasts. Two competing systems ran simultaneously for the first few months: Marconi-EMI's 405-line system and John Logie Baird's 240-line system, each with its own studio, transmitted on alternate weeks. The 405-line system was chosen in January 1937 and continued to operate here for years. The antenna, designed by Charles Samuel Franklin of the Marconi Company, is still in use. The original Studios A and B survive in the southeast wing, now exhibiting the historical broadcasting equipment. The borough's lightning-bolt coat of arms commemorates this moment, when television went out from a north London hilltop for the first time in history.

The events roster at Alexandra Palace reads like an anthology of twentieth-century popular culture. Led Zeppelin played two sell-out Christmas shows in the Grand Hall in December 1972, tickets priced at £1 each. The Grateful Dead played three nights in September 1974. Pink Floyd headlined the 14 Hour Technicolor Dream in April 1967, with John Lennon in the audience and Yoko Ono performing her piece 'Cut Piece'. The Brit Awards took place here from 1993 to 1995. Since 2008 the PDC World Darts Championship has filled the hall every December and January. The burnt-out shell of the Great Hall after the 1980 fire served as the location for Victory Square in the 1984 film adaptation of George Orwell's Nineteen Eighty-Four. Nick Cave recorded his 2020 solo concert film Idiot Prayer here. The Victorian theatre, dormant for decades, reopened in 2018 following a £27 million restoration. The palace keeps finding ways to remain useful — which may be the most remarkable thing about it.