The England Knights front-row was already under contract until the end of next season but has now committed until the end of 2023.
Huddersfield-born English came through the scholarship and academy system at the West Yorkshire club and has made 70 appearances since debuting n 2017, performing so well this term that he was invited to train with Shaun Wane's full England squad in April.
Although Giants failed to make the play-offs in Watson's first campaign in charge following his move from Salford Red Devils, plans are already well underway to remedy that next term.
Huddersfield have bolstered in the front-row with English set to play alongside England prop Chris Hill, the veteran who has signed from Warrington Wolves, and Seb Ikahihifo, who rejoins after two years on loan at Salford.
"I like the way the club is going," said English, with Giants also announcing the signing of Tonga stand-off Tui Lolohea from Salford earlier this week.
"Ian Watson is bringing something new to the club. The club have made a bold statement and backed him to rebuild this side, and being part of the plans for that rebuild is something I really want to be involved in."
Asked what he enjoys about working with the former Great Britain assistant coach, he said: "Ian Watson is so hands on; he lives and breathes Rugby League.
"He's really video orientated so he shows you how you can improve. He's making sure we're heading in the right direction.
"It's pretty special for the Academy Boys who have come through the club together. Some of us did Scholarship together, so we've been working and playing together for the best part of 10 years.
"It's special to work and train together with mates you've known for years and I'm proud of how we've all come through the system together."
Jake Wardle, Olly Russell, Sam Hewitt, the Senior twins and now Will Pryce are some of those who have come through the academy in recent seasons along with English.
Darnell McIntosh and Sam Wood have, too, although they are moving on to Hull FC and Hull KR respectively next term.
Watson said: "It's important we try to keep these guys, so to get Matty English to extend is a really big plus for us.
"The big thing from this season that's been really pleasing has been the young players coming through.
"They're getting a lot of game time and they're getting games thick and fast. There are a lot of young guys in there, and Matty English is one of them.
"Players learn by playing and Matty's been playing lots of Super League games and he's developing. Matty's been central to everything we've been doing this year.
"We're trying to bring in a mix of youth and experience to balance the side and help the younger players develop. We've seen what these younger guys can do, we want to develop them in the right way. You have to have a perfect balance and blend."