The incident took place late last night (2013 GMT) shortly after take-off, before flight VS025 returned as a precaution, the airline said. There were 252 passengers and 15 crew on board the aircraft.
A Virgin Atlantic crew member was recorded saying to Irish air traffic control that they had a "medical issue with one of the pilots after a laser incident after take-off".
Scotland Yard tweeted: "Aircraft forced to return to Heathrow after being hit by a laser strike".
A total of 414 "laser incidents" in the UK were reported to the UK Civil Aviation Authority between January and June 2015. The highest number of them - 48 - was at London's Heathrow Airport.