The Portuguese, exactly halfway through a three-year contract signed in 2016, is said to be in discussions over fresh terms to keep him at Old Trafford until 2021.
Mourinho won the Europa League, EFL Cup and Community Shield in his maiden campaign at United, and the Red Devils remain on course for success in the FA Cup and Champions League this time around.
Speaking to Sky Sports News, Neville backed the club's decision to open talks with the former Chelsea and Real Madrid boss at an early stage.
"I think it is great to see the club and Jose Mourinho committing to continuing down this path," he said. "One thing for certain is Mourinho has to leave the club as a success.
"I think it is too early to say whether he is going to stay six or seven years, but the job to do is to win the Premier League and it has to be done as soon as possible, so I'm glad that - unlike with David Moyes and Louis van Gaal - both parties are staying on the same path to get there.
"Yes, it is taking longer than the club and he will have wanted, but he's a manger who has always won and he's got to adapt the squad more, potentially with Alexis Sanchez in this window, then three or four more deals in the summer.
"I've always thought it takes about two-and-a-half seasons to really build a squad in the manager's image and I think this time next season he will be at that point where it really feels like his team."