The operator will begin running five flights a week - up from the current four - from April 7, 2014.
The extra flight will mean Icelandair can carry an additional 7500 passengers from Glasgow per year.
The service is particularly popular among holidaymakers using Reykjavik as a stop-off trip en route to the US and Canada.
Hjorvar Saeberg Hognason, Icelandair general manager UK & Ireland, said: "Our Glasgow route has always performed well, which is no surprise when you consider the size of the catchment area and breadth of industry. The extra capacity will allow us to offer even more connections to our growing number of destinations in North America."