Archaeological evidence from Hampstead Heath — Mesolithic flint tools, pits, postholes, and charred stones — indicates a hunter-gatherer community around 7000 BC. The land appeared in the Domesday Book of 1086 as held by the monastery of St Peter's at Westminster Abbey. From 1808 to 1814, the Heath hosted a station in the shutter telegraph chain connecting the Admiralty in London to naval ships at Great Yarmouth — signal poles flashing coded messages from this high ridge across the city below. The ridge itself, part of a sandy formation running from Hampstead to Highgate, reaches 134 metres at its highest point and provides views across London that Parliament has since protected by law.

In 1821, Sir Thomas Maryon Wilson inherited the estate and immediately sought to develop the land for housing. For nearly 50 years he pursued this goal, frustrated at every turn by the terms of his father's will. By the time he died in 1869, the campaign for public ownership had gathered serious momentum, led by the Commons Preservation Society, philanthropist Baroness Burdett-Coutts, and campaigner Octavia Hill. Parliament's 1870 purchase saved the Heath. A controversy in 1900 nearly undid the work: the Charing Cross, Euston and Hampstead Railway proposed tunnelling under part of the Heath for a new Underground line. The Heath & Hampstead Society opposed it. The Times published a strongly-worded editorial. But the railway company prevailed, arguing the tunnels were passing through impermeable clay more than 200 feet down. The line opened in 1907 and now forms part of the Northern line.

The chain of ponds along the Heath's eastern perimeter were originally reservoirs dug in the 17th and 18th centuries by the Hampstead Water Company, formed in 1692 to meet London's growing water demands. The ponds were created by damming Hampstead Brook — one of the sources of the River Fleet, which runs south underground to empty into the Thames. Today the ponds offer three open-air public swimming areas: the men's and ladies' bathing ponds, and a mixed pond. In 2005, the High Court ruled that members of the Hampstead Heath Winter Swimming Club had the right to swim in the mixed pond at their own risk. During a 2015 dam maintenance project, workers dredging the model boating pond found a vintage Ford Cortina at the bottom. It became a local landmark.

Karl Marx and his family walked the Heath regularly as their favourite outing. John Keats lived near the Heath and walked it while writing his Odes. Colin Wilson slept rough on the Heath in a sleeping bag, saving money while working on his first novel. Wilkie Collins opened The Woman in White with a scene set here. Bram Stoker placed vampires on it in Dracula. Taylor Swift mentioned it in "So Long, London." In 2023, the City of London Corporation returned sheep to the Heath for the first time since the 1950s — five rare-breed Norfolk Horn and Oxford Down — to enhance biodiversity through controlled grazing. The Heath, which has absorbed centuries of use and survived repeated attempts at development, continues to absorb whatever London asks of it.