After eight years with Ferrari, Massa is to leave a marque where he has at least enjoyed the prospect of winning races for a team that has scored just one point this season.
Without doubt Williams are currently enduring the worst campaign in their illustrious history, with all their titles and triumphs a distant memory.
But in visiting the Grove factory recently before putting pen to paper on a deal, Massa insists he saw enough to believe Williams can be a force again.
"I'm very enthusiastic and happy to have signed a contract with Williams," said Massa, speaking ahead of this weekend's United States Grand Prix in Austin.
"I'm really looking forward to this challenge in my career. I'm very motivated. They are a big team, and I was really surprised with what I saw.
"They have the infrastructure to do a good job, and they are trying to put the pieces together.
"They have been changing so many pieces inside the team to try and get themselves back to where they were. They are a competitive team with a long history in Formula One.
"This is a very difficult time for them, and this is a very difficult championship.
"But there are so many things going on inside the team, with so many people that are different, working for next year's car.
"They also have the Mercedes engine, which I am very happy with because people have been talking very well about Mercedes engines for next year.
"Aerodynamics remains an important point, and that is something they are changing in the way they are working on that for next year.
"They really are trying to get back to being a competitive team, so they are changing even the drivers.
"So many things are changing inside the team which is interesting and important, not just for next year, but for the long-term future."
Massa has revealed Williams was not the only team on his radar after it was announced he would be leaving Ferrari.
Whilst it was no secret Massa held talks with Lotus, the fact he was also in discussions with McLaren has come as a surprise.
"I spoke not only with Williams, but also Force India and McLaren," revealed Massa.
McLaren this week axed Sergio Perez in favour of promoting their develpment driver Kevin Magnussen.
Massa added: "To be honest, with everything that was happening and with everything I was looking with regard to the future, I am more convinced Williams is the right choice.
"A strong choice would have been McLaren, but then McLaren took a different direction for them.
"So in my opinion Williams is the most constructive team for the future, and I really believe my choice is the good one."