The additional flights will operate from 30 March 2025 through to 25 October 2025, complementing its existing four-times-daily Heathrow service.
It means SIA will operate five daily London-Singapore services during summer 2025, which it said would "support higher demand for air travel to several popular destinations".
However, citing wider capacity adjustments across its European network, SIA will suspend its Singapore-Houston service, which operates via Manchester, from 1 April 2025.
It will, though, maintain its five-times-weekly Singapore-Manchester services.
SIA acting vice-president marketing planning, Dai Haoyu, said the carrier regularly reviewed its network and routes "to align capacity with demand".
"These adjustments, ahead of next summer, cater to the higher demand to several destinations, particularly during the traditional mid-year peak travel season, enabling our customers to confidently make their 2025 travel plans," he said.
