The garden is London's first permanent tribute to the 1,523 passengers and crew who died after the ship struck an iceberg in the North Atlantic during its maiden voyage in 1912. Its opening coincides with an exhibition of artefacts from the wreck on display at the museum.
Mrs Haisman - who at 98 is the oldest living survivor - was 15 when she accompanied her parents on the luxury liner to start a new life in Seattle.
She recalled that there was no panic at first and she managed to get into a lifeboat, but then the scale of the calamity began to dawn. "Most of the men jumped overboard into the sea. Those who could swim swam and those who could not sank. There was no hope for anyone."
She described the garden, with its specially commissioned granite monument, as a "beautiful" tribute to those who died.