The Laver Cup Open Practice Day will be staged on September 22 at The O2 in London.
Fans will get the chance to watch Federer and other tennis greats including Sir Andy Murray, Novak Djokovic and Rafael Nadal from Team Europe and Team World during their final on-court practice for the competition.
Tickets go on sale on Monday August 22.
The event will raise money for two organisations of which Kate is patron – Action for Children and the Lawn Tennis Association (LTA), whose charitable arm is the LTA Tennis Foundation.
The collaboration between the Laver Cup, which was co-founded by Federer, and the two charities was Kate’s idea, Kensington Palace said.
The Laver Cup will also host a day of tennis in east London, attended by Kate and Federer, for children aged eight to 15 drawn from those supported by Action for Children and youngsters from the local area who are part of the LTA Serves programme.
Federer tweeted he was excited to announce the Laver Cup was partnering with the duchess this year, adding: “Thank you for your support, and I look forward to seeing you in London!”
Kate, who is a passionate tennis fan, is patron of the All England Lawn Tennis and Croquet Club (AELTC), the organisation which stages Wimbledon.
Federer is Prince George’s favourite player, and the 20-times grand slam champion has given coaching tips to the prince in the past, playing him after meeting the royal youngster at the home of Kate’s parents in Bucklebury, Berkshire, in 2019.
The Swiss player revealed George had a “good technique”.
Federer – a long-time friend of the Middleton family – and his wife Mirka were guests at the wedding of the duchess’s sister Pippa in 2017.
And Kate once confessed in a BBC documentary that Federer was her mother Carole’s secret crush, saying: “Roger is my mother’s heartthrob. I don’t think she will mind me saying that. I think he probably knows that too.”
Kate presented Federer with his runners-up plate after his 2019 Wimbledon men’s final defeat by Novak Djokovic.
Known for her competitiveness, Kate played a practice session with US Open women’s champion Emma Raducanu during a homecoming event in September last year.
Kensington Palace said the duchess is “passionate about supporting grassroots tennis and encouraging young people from all backgrounds to become involved in the sport”.
Donations raised for Action for Children will help provide practical and emotional care and support for vulnerable youngsters and their families, with the charity also making sure they can have fun through activities and days out.
The money will also fund 50 new LTA Serves tennis coaching programmes for children in some of the most deprived areas of the country, including near The O2 in London, as a lasting legacy of the Laver Cup.
The prestigious cup was set up in 2017 in honour of Australian tennis legend Rod Laver.
Played on a distinctive black court, the three-day team competition sees rivals become teammates as six of the best players from Europe compete against six of their counterparts from the rest of the world.
Federer will join Sir Andy, Djokovic, Nadal, Casper Ruud and Stefanos Tsitsipas in Team Europe to face America’s Taylor Fritz, Canada’s Felix Auger-Aliassime and Argentina’s Diego Schwartzman, among others, from Team World.