The event is being staged on the back of the huge success of the Barney Curley Day at the track last September, a card which featured Dettori's first visit to the venue and raised over €100,000 for Direct Aid for Africa (DAFA), the charity established by trainer Curley, who died in May 2021.
It is hoped the new competition can become an annual event. Dettori is to manage the away team with Mullins taking charge of the home jockeys.
"I'm looking forward to coming back to Bellewstown on Wednesday, September 28 for the Barney Curley Charity Cup in memory of my great friend and to support his wonderful charity DAFA," said Dettori.
"I was delighted to win the 2016 Irish St Leger for Willie Mullins on Wicklow Brave, but I'll be selecting my team very carefully to try to beat Willie and his home team.
"Both of us will want to win the challenge, so I can guarantee it's going to be ultra-competitive."
Mullins said: "Frankie Dettori is one of the most competitive jockeys in the world and I know Barney was such a good friend of his, so the home team jockeys and I will have our work cut out for us.
"Barney was one of the great racing characters and did such fantastic work with DAFA, so I'm honoured to support the inaugural Barney Curley Charity Cup and hopefully we can keep the cup at home. It's going to be a great day."
Seven riders on each team will face off over two races with points awarded and the team which accrues the most points will take the title.
Tickets can be bought at www.bellewstownraces.ie and cost €20 with €10 going to DAFA.