Kolisi and reigning World Rugby Player of the Year Du Toit will be the headline acts for the team in 2020, with lock Eben Etzebeth and centre Damian de Allende having departed for France and Japan respectively.
Hooker Scarra Ntubeni and utility back Dillyn Leyds, who both played for the Boks in 2019, also penned contracts for the next two years.
“We know what these players offer on and off the field, the challenge now is to get the most out of their considerable talents,” new Stormers coach John Dobson said in a statement on Tuesday.
Kolisi, back training after a whirlwind few months that included lifting the World Cup trophy, believes the Stormers are in good shape.
“I have been playing with some of these guys my whole career and we are all looking forward to reaching new heights in a Stormers jersey,” he said.
“We have a strong group of senior players and talented youngsters coming through all the time, which is what we need to reach our goal.”
Western Province CEO Paul Zacks admits new salary cap restrictions placed on South African sides have made the process of developing the squad harder.
“While the introduction of the new contracting model, salary caps and the number of senior players that we can contract has made it a challenging process, I am most pleased to confirm that we have managed to retain the majority of our senior players for 2020 and beyond,” he said.