Having defeated Formula One legends Sebastian Vettel and Michael Schumacher in earlier rounds, Grosjean had few problems against Le Mans expert Kristensen, winning 2-0 in the best-of-three final before a big crowd on Sunday.
Grosjean, 26, won the crown in his second ROC appearance, while 45-year-old Kristensen has failed to win the title in 13 attempts.
Eight-time Le Mans champion Kristensen also reached the final last year before losing to another Frenchman, Sebastien Ogier.
On Sunday, Kristensen defeated Ogier in the quarter-finals, while Grosjean finished off Vettel in the last eight and beat Schumacher in the last four.
“It’s been a tough end to the F1 season but I finally got back on the podium,” Grosjean said. “It’s great to get this win before I head off for a holiday. Thanks to everyone in Thailand because the welcome has been fantastic.”
Kristensen said small mistakes cost him the title this year. “Romain is a deserved winner,” said Kristensen, who beat former Formula One driver David Coultard in the semi-finals.
“I’m getting closer every year. It was a small gap between us in each of the heats. I made small mistakes but that’s the challenge of the Race Of Champions in jumping into different cars,” he said.
Grand prix legend Schumacher was knocked out by Grosjean in the semi-final of the headline event while three-time Formula One champion Vettel stumbled at the quarters for the second year running.
But it was not all bad news for the German superstar, as he claimed the ROC Nations Cup on Saturday for the sixth time in a row with compatriot Schumacher.
Thailand hopefuls Nattavude Charoensukawattana and Tin Sritrai failed to reach the knockout stages.
Thailand will host next year’s edition of the Race of Champions under a two-year contract, and Thai officials hope the race will lead to the country getting approval to organise a Formula One race.
They say Formula One supremo Bernie Ecclestone has agreed in principle for the kingdom to host a Grand Prix in 2014, but a formal deal has not yet been reached.