Almost 70% of the 3,328 riders who entered the 2015 Etape Loch Ness in April were from outside the region, Mackay Consultants Inverness said.
The firm examined how much those people were likely to have spent on food and accommodation.
This year was the second time the cycling event had been held.
As well as the economic boost, it raised £228,000 for charity.
Spending by people who travelled to take part in a major cycling event generated £743,000 for the Highlands' economy, according to consultants.