The current tenth run of The X Factor was rumoured to be the last, but in June ITV boss Adam Crozier restated the broadcaster's commitment to what he called "a very important programme for ITV".
Cowell said: "I am thrilled that we have extended our deal with ITV for Britain's Got Talent and The X Factor.
"They have been fantastic partners and we have some exciting new plans to take the shows to the next level."
ITV Director of Television Peter Fincham added: "Britain's Got Talent and The X Factor are two of the most popular and most talked about shows on TV. They set the gold standard for entertainment production.
"We're pleased to announce this deal, which will see them continue to be an important part of ITV's schedule."
Britain's Got Talent will return to ITV next spring for its eighth series and The X Factor's 11th run will begin in the autumn.
Spinoff shows The Xtra Factor and Britain's Got More Talent will continue on ITV2.
FremantleMedia UK CEO Sara Geater said: "We are delighted to be continuing our relationship with ITV and Syco.
"Britain's Got Talent and The X Factor are two of the UK's most successful shows, which is a testament to the talented production teams behind both series, and we look forward to bringing viewers more world-class entertainment for a further three years."