Brian Thompson was shot several times outside the Hilton Hotel in Midtown Manhattan where he was set to speak at an event later in the day.
Mr Thompson, 50, was rushed to hospital but later died. The attacker fled after the shooting police said.
Officers released two images showing the gunman shooting and then fleeing on a bicycle. A $10,000 reward has been issued for information leading to his capture.
A spokesperson for Hilton said they were “deeply saddened by this morning’s events in the area and our thoughts are with all affected by the tragedy”. An announcement was made to attendees that the event was being ended early.
UnitedHealthcare is the largest provider of Medicare health insurance plans in the country.
New York Police Department officials said a 50-year-old man had been killed in the area but did not confirm his identity, local media reported.
The hotel where Mr Thompson was shot is a short walk from tourist sites such as the Museum of Modern Art and Rockefeller Centre.
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