The fresh terms will keep the Croatia international, 28, forward at the San Siro until 2022.
Perisic spent much of the summer seeing his future being called into question, amid intense talk of interest from United.
Inter, though, maintained throughout that they had no intention of parting with him and have now been able to put an extended deal in place.
A statement on the club’s official website read: “Inter are happy to announce the extension of the contract of Ivan Perisic, who will continue to wear the Nerazzurri colours until June 30, 2022.
“Born in Split on 2 February 1989, Ivan arrived at Inter in the 2015-2016 season.
“He has made 81 appearances in Serie A, national cups and Europa League so far. But it does not end there...”
He netted 11 times in all competitions last season, while providing eight assists in Serie A.
The talented forward has already conjured up three efforts for grateful team-mates this season to top the early creativity charts.
Perisic is delighted to now be in a position to focus his full attention on matters on the field, telling Inter's website: “It’s a special day, it’s certainly emotional and I’m happy after the stress of this summer.
"Now, we can look forward and I’m only thinking about Inter. After signing, the pitch is the only thing left for me to think about.
“For a long time I didn’t give quotes, I can now say that I had already spoken with [Luciano] Spalletti in pre-season and he told me that I can be an even better player with him.
"[Samir] Handanovic also spoke to me about Spalletti from their time at Udinese and he only had good things to say about him.
"We did well in our first two matches and now we have to continue in the same way. There are always a lot fans who turn up and it’s better for us like that. It will be easier with their support.”
Inter have taken maximum points from their opening two fixtures to sit joint-top of the table with Juventus.