A total of 6.7 million passengers travelled through Heathrow in May, up 3.1 per cent on the same month last year.
At the same time, wedding watchers from the US travelling to nearby Windsor pushed up passenger numbers five per cent on North American flights.
The figures come as Parliament prepares to vote on expanding Heathrow.
Support for the project remains “overwhelming”, claims the airport, with the latest polling shows 75 per cent of MPs back expansion at Heathrow, alongside a united chorus of support from Britain’s major business groups and trade unions.
Domestic flights also saw an uplift, boosted 5.5 per cent, as more passengers filled flights to Aberdeen, Edinburgh and Leeds.
Over 144,000 metric tonnes of cargo passed through Heathrow in May, the 22nd consecutive month of record growth at the UK’s largest port by value for non-EU trade.
Heathrow chief executive John Holland-Kaye said: “We have a robust plan to expand Britain’s hub airport, unlocking billions in growth and creating tens of thousands of new skilled jobs – from Plymouth to Perth and Swansea to Southend.
“With strong cross-party support and a united voice from business and unions – MPs must finally seize the opportunity to expand Heathrow and secure a prosperous future for all of Britain.”
Heathrow welcomed the arrival of new direct services to the cities of Wuhan and Sanya, operated by China Southern, last month.
The airport’s connection to Sanya is a first for Europe.
The routes will allow for 6,000 metric tonnes of additional cargo capacity and over 110,000 new seats for passengers annually.