"It has been a good quarter for Norwegian with positive growth throughout our route network, particularly on our long-haul network," chief executive Bjørn Kjos said in a statement.
Net profit in the second quarter more than doubled from a year ago to 325 million kroner (36.7 million euros, $40 million) as the load factor, a measure of how full planes are, rose five percentage points to 85 percent.
The number of passengers rose by nine percent to nearly seven million, with London's Gatwick Airport -- where Norwegian was already the third largest airline -- posting the biggest gains, followed by Oslo and airports in Spain.
Norwegian is one of the few low-cost carriers to have ventured into long-haul flights, and has more than doubled the number of passengers in the segment to 324,000, giving it a load factor of 91 percent.
The group will soon increase the number of long-haul routes -- all of which are currently operated between Northern Europe and North America, the Caribbean and Bangkok -- from 21 to 28, including one between Gatwick and Boston.
Last month it announced the launch of its first routes not serving Europe, between the US and the French territories of Martinique and Guadeloupe.
Revenue grew 16 percent from a year ago to 5.86 billion kroner. A weakening of the Norwegian krone against the dollar and the euro was more than offset by a decline in fuel prices.