Revenue per passenger kilometres at the budget carrier grew 48 percent year-on-year, exceeding an average forecast for a 39.9 percent rise in a Reuters poll of analysts.
Norwegian shares were up 3.7 percent by 0738 GMT, beating a 0.6 percent drop in Oslo's benchmark stock index.
Norwegian last month raised 1.3 billion Norwegian crowns ($165 million) in a share issue partly to pay for rapid fleet expansion as it tries to crack the market for transatlantic travel by undercutting established rivals.
"Even though Easter strongly impacts this month's figures, we have a solid passenger growth," Chief Executive Bjoern Kjos said. "The international growth continues, and at the same time, more people are flying with us in Scandinavia".
The company's passenger capacity grew by 44 percent in March from the same month of 2017, while its load factor - a key airline measure of how many available seats have been sold - increased to 86.7 percent, beating the 84.9 percent predicted.
Norwegian's yield, or revenue per passenger kilometre, rose to 0.35 crowns, as expected, from 0.31 crowns in February and 0.34 crowns a year ago.
The combination of a higher yield and strong growth would boost March revenue by 54 percent year-on-year, broker Pareto Securities said, adding this was 8 percent more than expected.
Pareto, which holds a "buy" recommendation on the stock, was among the group of investment banks that raised money on behalf of Norwegian last month.
Danske Bank, which rates the shares "sell", said the turnaround in yield was encouraging, although it would likely see a drop in April as the effects of Easter wear off.