Gatwick handled 6.6% more passengers – or 138,300 – in January over the same month last year.
The increase meant a total of 2.2 million passengers used the airport in the month, with European routes seeing the biggest growth.
More than 1.4 million passengers flew to European destinations – an increase of 8% over January 2013.
The majority of the increase was on flights to key business routes to cities such as Stockholm, Istanbul, Moscow and Copenhagen.
This was tempered by fewer passengers on charter flights to European leisure destinations, reflecting the longer-term market move towards scheduled, low-cost airlines, the airport said.
Other long-haul growth was up 11.3%, mainly as a result of increases on leisure routes such as Thailand and Sri Lanka. This was complemented by growth on long-haul business routes such as Dubai.
A 13.4% slump in transatlantic traffic was mainly due to US Airways ceasing services from Gatwick earlier in 2013.
The launch of three routes by Norwegian to New York, Los Angeles and Florida are expected to help reverse the trend of lower traffic to this region.
For domestic traffic, increases on the Belfast, Glasgow and Isle of Man routes were offset by the withdrawal of a route to Manchester.
The airport’s chief financial officer Nick Dunn said: “We saw steady growth to Europe in January, which is by far the dominant market for business and leisure passengers travelling from London and the southeast.
“Alongside European growth, however, we continue to see strong performance in long-haul travel, particularly on established routes to the Middle East, Far East and the Indian sub-continent.
“Next month we will be welcoming Emirates’ daily A380 services to Dubai and Air China’s flights to Beijing to further strengthen these routes and provide even greater choice and convenience for passengers.”