Mercedes have won the constructors title eight times since partnering with Petronas in 2010, though drivers Lewis Hamilton (37) and George Russell (24) are yet to win a race this season.
"Today we are doing something a little bit unusual – announcing a partnership that will begin in four years' time," said CEO and team principal Toto Wolff.
"This sends an important message: our team and Petronas are no longer just partners, we are family, and we will be one team for many more years to come.
"From 2026, advanced sustainable fuel will be at the heart of F1 performance – and this gives us a fantastic opportunity to demonstrate our expertise in this domain, through both the power unit and Petronas Fluid Technology Solutions."
Wolff, Hamilton and Russell are in Kuala Lumpur ahead of the Singapore Grand Prix, which will take place this weekend at the Marina Bay Street Circuit.
"I feel like this has been a year of growth. And I think it's been empowering to have an experience like this," Hamilton told reporters.
"There's people on our team that have joined, for example, in the seven or eight years of dominance that we had and have only known winning. And so this has been a good experience for all of us."
Mercedes are third in the championship, 35 points behind Ferrari but a massive 174 adrift of runaway leaders Red Bull.
"I think if we can achieve that second place in the constructors' championship, there'll be a huge boost for all of us back at the factory, and also probably quite a huge blow to our rivals in Ferrari," said Russell.
"Psychologically, it can be quite important, but nevertheless to see that improvement we've made through the season... I think it's looking really good going into next season."
Ferrari started the season strongly, with Charles Leclerc (24) winning two of the first three races and finishing second in the other, but have made driver and strategy errors as well as suffering reliability issues.
Russell has been on the podium in four of the last five races.