Webber said he had signed a multiyear deal with Porsche to race prototype-style sports cars in the 24 Hours of Le Mans and in the World Endurance Championship series.
"I'm very much looking forward to this new challenge," Webber said on his website Thursday, adding that "it's an honor for me to join Porsche."
The announcement came as Formula One prepared for Sunday's British Grand Prix at the Silverstone circuit.
Webber, who began racing in Formula One in 2002 and joined Red Bull Racing in 2007, has nine career victories and 36 podium finishes overall.
The Australian has yet to win this year and is fifth in the Formula One championship standings, 63 points behind the first-place Vettel, who's gunning for a fourth consecutive world title.
Talk of Webber possibly leaving Formula One first surfaced in March after the Malaysian Grand Prix. Webber was leading late in the race but Vettel defied team orders and passed Webber for the win, leaving Webber infuriated.
But Webber said that incident had no bearing on his decision to leave. "I've had a personal plan and I've stuck to it," he said. "This is the next chapter."
Vettel, meanwhile, said of Webber on Formula One's website that "I have enormous respect for him as a driver" and that "off-track I would say that many things" about problems with their relationship "have been hyped more than they should have."