This year marked his fourth full campaign in the world championship and his second consecutive run with the Honda-powered squad which underwent a rebrand in 2020.
The Frenchman hailed qualifying consistency on Saturday and solid points scoring come Sunday, finishing ninth in the drivers' championship.
The highlights of his season included a third place finish in the Azerbaijan Grand Prix as well as a front row start in the inaugural Qatar Grand Prix.
The Red Bull-affiliated driver often found himself at the pointy end of the mid-pack battle, nine times finishing inside the top six.
Gasly failed to record points in seven grands prix out of 22 but was otherwise happy to score more than 100 points for the first time in his career.
“It's been incredible,” said Gasly in a fan Q&A video prior to the season-ending Abu Dhabi Grand Prix.
“I must say, as much as I was looking forward to this year and our expectations were also quite high at the start of this year, we still overperformed to what we expected, especially in qualifying.
“We've been really good on Saturdays. Sundays as well. One hundred points this season is better than what we could have imagined.”
“Clearly my best season in F1,” he added.
“I think I've just improved in all aspects with more experience, four seasons in F1, especially continuing with the team I think has helped me a lot with the relationship – the way we work together, also having more responsibility in AlphaTauri has kind of helped me.”
Gasly noted a change of guard in the AlphaTauri ranks with the arrival of Japan's Yuki Tsunoda to the team, which came as a result of Russian driver Daniil Kvyat parting company.
The Frenchman said he embraced his seniority within the team to lead the way with its direction of the AT02.
“I knew I would have more responsibility to lead the team in the direction, the correct direction, let's say, and I'm really happy with the job we've done,” said Gasly.
“Obviously, you can always improve. I think with more experience, even this year was my best year, in terms of consistency, in terms of speed, in terms of working with the guys.
“I still think next year is going to be even stronger and the year after. Being in F1, it's quite particular because we don't train so much that you keep improving the entire time.”
AlphaTauri improved on its 2020 season in the constructors' championship, climbing from seventh to sixth.
The team narrowly missed out on fifth in the constructors' title race, falling 13 points shy of Alpine.