Captain Trine Ronning converted a free kick in the 15th minute and striker Isabell Herlovsen netted a quick first half brace as the Thais struggled to cope with their more muscular and skilful opponents.
Despite the warm conditions, Norway kept up the pressure in the second half, when teenage forward Ada Hegerberg added a goal and Maren Mjelde then missed a penalty.
"Our physical strength is better, we have a more tactically mature team and that brought us the win," said Norwegian coach Even Pellerud.
Norway, ranked 11th in the world, were one of the early women's powerhouses and won the World Cup in 1995. But in recent years they have been largely eclipsed by Germany and the United States and did not qualify from their opening group in the 2011 tournament.
This year's World Cup marks the first time that 24 teams are taking part, up from 16 last time.
Thailand, ranked 29th, missed a good chance early and visibly lost confidence against a much more experienced Norwegian side.
"We learned how women's soccer is played at the international level ... We'll have to develop our team a lot more," Thai coach Nuengrutai Srathongvian told reporters.
Norway's third goal epitomized the team's dominance. Solveig Gulbrandsen found herself confronted by two defenders but effortlessly pushed past them and sent in a cross that Herlovsen converted with a close range header.
Pellerud criticized his team, saying they needed to pass better in their opponents' half and also to convert more of their scoring opportunities.
The Norwegians spurned several excellent chances. As well as Mjelde's penalty miss, Herlovsen had a goal chalked off for offside and Hegerberg twice hit posts.
Norway's next game is on Jun.e 11 in Ottawa against top-ranked Germany, one of the favourites to win the tournament. Thailand will play fellow outsiders Ivory Coast the same day.
Germany take on 67th ranked Ivory Coast in the second Group B game later on Sunday in Ottawa.
(Reporting by David Ljunggren, editing by Gene Cherry)
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