The 67-minute victory came partly because Simon fell victim to a knee problem, a day after playing what he called some of his best tennis to reach the final. He cut a hugely despondent figure afterwards.
Gasquet, 26, last tasted title success on clay in Nice in May 2010, and had lost three finals since then, including Estoril and Toronto this season.
"I'm glad to win a title but it's tough to do it like this against another French player, a friend of mine," said the winner. "I have to be pleased to win but it was a little bit strange.
"I've had some tough matches this week, so this seventh title is a big one for me.
"I've played and lost some finals over the years since my last one, so it's always good to finally win one. It was a good win for me here, a big comeback week."
Gasquet, seeded second in Bangkok, said he knew nothing of Simon's condition until his opponent took treatment trailing a set and 4-1 down.
Simon, the fourth seed, said that he was not sure if he would be fit for Tokyo, which starts straight away.
"I'll have to see how I feel and how I practise there," he said.
"I was playing some of my best tennis in the semi-finals -- in the final it ends like this,' said the disappointed 27-year-old, who has split with coach Thierry Tulasne to go it alone for the foreseeable future.
Tulasne was in the stands for a farewell all week but will not travel to the Japanese capital.
"It would have been nice to win this one for him, but it was not to be," said Simon.
"I just can't be optimistic any more, I just have to live with this kind of uncertainty," said Simon, who has also had back and shoulder problems in recent seasons.