Almiron is enjoying his best run of form since joining Newcastle from Atlanta United in January 2019.
The Paraguay international has scored 10 of his 19 Premier League goals this season for the Magpies, who are challenging for an European spot under Eddie Howe.
Almiron was voted Premier League player of the month back in October.
The 29-year-old will hope to celebrate his new contract by helping Newcastle beat Manchester United in the Carabao Cup final at Wembley on Sunday.
He told the club's website: 'I am very happy to sign a new contract with Newcastle. I felt at home at Newcastle from the beginning.
'I've felt very welcomed and I feel like part of the family, so I am very happy to stay here and I am going to keep giving everything on the pitch to thank the people of Newcastle.
'The truth is that I've worked really hard since I came to Newcastle to improve my level and to be where I am at the moment, and I also thank the staff and my team-mates, who have helped me a lot during these four years.
'I think this is a reward for that hard work and I am very happy. On Sunday, we have a very important match and while the new contract makes me really happy, the most important thing is that we celebrate this contract with a victory on Sunday.'
Delighted with Almiron's new deal, manager Howe added: 'Miggy is a hugely important part of our squad on and off the pitch and I'm very pleased to see his contribution acknowledged in this way.
'I'm delighted we'll continue our journey together.'
