The pair will help celebrate the festival’s 21st birthday, heading a line-up which includes chart-toppers Sia, Little Mix, Jess Glynne, Years & Years and Bastille.
Others announced so far include David Guetta, Faithless, Kaiser Chiefs, John Newman, Jake Bugg, Rita Ora, Halsey, Tinie Tempah, Example, Craig David, Katy B, Travis, DJ EZ, Sigma, All Saints and Lethal Bizzle.
The full day-by-day line-up will be announced on Wednesday at 10pm, immediately following the Brit Awards.
Both Rihanna and Justin are scheduled to perform at the Brits, although concerns have been raised that Rihanna could cancel after pulling out of some of her UK stadium dates for her Anti Tour.
She was also forced to cancel her Grammy Awards performance due to ill health.
Rihanna, Justin, Sia and Guetta will be V Festival exclusives as they will not perform at any other UK event this summer.
V Festival takes place across two sites – in Hylands Park, Chelmsford, and Weston Park, Staffordshire. This year’s festival will be held over the weekend of August 20 and 21.
Rihanna will headline at Weston Park before moving to Hylands Park, swapping with Justin as he heads in the opposite direction.
The festival is also introducing a new BBC Radio 1 Summer Of Dance stage on Friday night across both festival sites, with further details announced on March 4.
Tickets for V Festival will go on sale on Friday February 26 from 9.30am