By Agence France-Presse
NGO Medicina Sociale approached the management of the new outlet after the opposition of some cardinals to it being allowed to open hit the headlines at the end of last month.
"They got back to us inside 24 hours," spokeswoman Gianluca Scarnicci told AFP on Thursday.
From next week, Medicina volunteers will distribute meals made up of a double cheeseburger, an apple and a bottle of water to homeless people in and around the Vatican, every Monday lunchtime.
"We will be able to go up to 1,000 meals but we are starting with 50 on Monday," Scarnicci said.
The new McDonald's branch is housed in a building a stone's throw from St Peter's square. It is owned by the Vatican's real estate agency ASPA.
Opposition to its opening was spearheaded by a group of cardinals who occupy the upper floors of the historic building.
Other residents have complained that the fast food joint will bring down the tone of the neighbourhood but it has been a hit with many tourists.
Pope Francis has come under fire over the lease with critics saying he could have blocked it given his regular criticism of multinationals.
The decision to rent the space for a reported 30,000 euros per month is, however, consistent with Francis's determination to ensure the Vatican's huge property portfolio is run on commercial lines.
The pope has himself ordered several initiatives to help the homeless in Rome, including opening up showers next to St Peter's and distributing sleeping bags.