The current championship leader announced his decision to stay with the team on the eve of this weekend's Catalan Grand Prix, with the deal having been signed "a few weeks ago".
Although he said on Thursday he had been tempted to move to a different team, the Frenchman explained that he was "super happy" with the decision to stay with Yamaha because the team "know where they need to improve".
Quartararo also said Yamaha is working to direct extra resource to its engine department in a bid to bring more power to the 2023 bike, an area he has previously expressed disappointment in.
He said: "It was not an easy decision and we took a little bit more time to evaluate all the project. At the end, Yamaha make a lot of effort, bring a lot of new people and they know where they need to improve.
"The last two or three years, they were in some areas to another and know where they need to improve and they know clearly it's the power.
"I'm super happy because they really understand, they're doing the best to find what we are missing and I believe in the project, so that's why we took the decision. I will not say days, but a few weeks ago, and of course it was a good decision."
He added: "My first goal is to have the best bike and the best project, like I said before, and they convinced me because they bring new people, they are working super hard, and they know exactly where they need to improve.
"But in the past maybe they were working on a few areas, but they don't really maybe accept that the bike was more slow than the others.
"And now they know and they clearly work on this weak point, that's what made me take the decision to stay in Yamaha."
Quartararo has been the standout Yamaha rider in 2022, scoring a win in Portugal and three other podiums to lead the standings by eight points. The combined points total of teammate Franco Morbidelli and RNF Racing duo Andrea Dovizioso and Darryn Binder is just 34 to Quartararo's 122.
During the Austin weekend, Quartararo's manager revealed rival teams had been in touch, while Quartararo himself said earlier in the year his future was open having been unhappy with a lack of progress made by Yamaha in finding more speed from its engine.
Quartararo said on Thursday that part of the reason for a delay in him re-signing was because "at one stage my head was going to one side."
But reassurances made to him by senior management, coupled with his recent good results including a win at Portimao, convinced him to stay for another two years.
He said: "As you can imagine, we were not talking only to Yamaha, and I took that much time because at one stage my head was going to one side, then one week later I wanted to go there, and it was a little bit difficult.
"I think of course what happened about these engineers going to the engine side and myself doing great results and knowing that I could not do more because of [a lack of] power [in the] engine.
"Of course I know that what they are pushing in is to bring more power and I feel good on the bike, so that's what made me take the decision to follow."
Yamaha will only field two bikes in 2023 after RNF Racing announced it would switch to Aprilia machinery for the next two seasons.
Quartararo's teammate Morbidelli also has a contract for 2023, having agreed a two-year deal with Yamaha late in 2021.
