14 of those appearances have come this season, with Leeds sitting 15th on the Premier League table.
Struijk's previous contract would have expired in the summer of 2024.
Born in Belgium, Struijk has played for Netherlands at youth level and was included in Louis Van Gaal's provisional squad for the Qatar 2022 FIFA World Cup but did not make the final cut.
The 23-year-old has made 77 appearances since joining Leeds from Ajax Amsterdam in January 2018.
A club statement added: "The club are pleased to have secured Pascal’s future, meaning he will continue to help the side throughout the rest of this season, when it gets back underway after Christmas, and then over the coming years at Elland Road."
Speaking to the club's official website about his new contract, Struijk said: "It feels really good. I've been at the club for a while now and I'm really happy to extend my journey.
"Like in the song, there have been a lot of ups and downs, we didn't get promotion in my first year, we did in the second, we had a really good first season in the Premier League and in the second season it was tricky, but we still managed to stay in it.
"Now we are here, we want to finish the second half of the season as well as possible and then go again."
Struijk added: "I came here with one target and that was to become the best version of myself and to play in the Premier League, because it is the best league in the world.
"The journey so far for me has been really good, I think I've grown as a person and as a player. The more I can add to my package as a player, the better I can become, I want to get better every day by work hard in training and see how much I can improve.
"Day to day, this is an amazing club and the fans that come with it too are amazing as well. The whole group of players are a really good group, I come into training every day with a smile, so it was a really easy decision for me to extend my contract because I'm so happy here."
Leeds United return to Premier League action against Manchester City on Wednesday.
