McCartney: Inspired by heroic rescue efforts
Sir Paul is to approach music colleagues such as Mick Jagger and Neil Young and has already secured old band mate Ringo Starr for the gig.
The show is to take place in New York's Madison Square Garden on 20 October and is a very personal project for Sir Paul.
Sir Paul was in New York when the attacks happened, and he told BBC London Live he, like the city as a whole, had been deeply affected by it.
"Most people are in quite a sombre mood. People are being a bit more polite. You hear the word 'unbelievable' a lot," he said.
He spoke of his visit to "ground zero" and how he was moved by the "heroism" of the firemen.
"My dad was a fireman in World War II in Liverpool," he said, "so I have a lot of respect for firemen. You and I want to run out of a building and they have got to run in."
Sir Paul said that he was planning to do something for the victims of the attacks when the offer of the concert came up. "I thought I'd do that," he said. "Mainly, in my case, for the firemen's families."
Live audience
The concert will take place in front of some 18,000 people - unlike the fund-raising telethon at the weekend which did not have a live audience for security reasons.
The all-star telethon raised $150m (£103m) for charities helping victims of the 11 September attacks.
A CD of music from that event featuring Bruce Springsteen, Mariah Carey, Paul Simon and Billy Joel among others is set to be released.
The organisers of the event are working to clear rights to the music, which was originally only approved for the one-off show - America: A Tribute to Heroes.
"It's being done as soon as possible. They're working on it as fast as humanly possible," a spokeswoman said.
Personal sum
Other artists who performed for free included Celine Dion, Sting and The Dixie Chicks.
Stars such as Tom Cruise, Tom Hanks and Julia Roberts helped take telephone pledges for the fund.
Roberts, like other film and music stars, also contributed a personal sum, $2m (£1.35m), to the United Way fund, which will also receive all proceeds from the compilation album.
The Academy of Motion Picture Arts and Sciences, which presents the Oscars has said it will donate $1m (£.67m) to charity.
Cinema-goers in the States also raised $3m (£2.03m) during a Victims' Benefit Day on Tuesday.
All tickets sales were donated to charity and film distributors also waived payments so the maximum amount of money could be divided between the United Way and the American Red Cross.
Michael Jackson is continuing to work on his own charity single alongside Destiny's Child, Seal, Tom Petty and Boyz II Men.
The track, What More Can I Give, was written and composed by Jackson to aid the fundraising drive.