The London Heroes Return event will take place in Trafalgar Square, beginning at 1pm.
The area will be open from 11am and is free, although members of the public are advised to arrive early as capacity is limited.
However, a big screen at the rear of the square will be available if the area is full.
Entertainment beginning at midday and the main show at 1pm.
When does it end?
The event ends at 2.30pm.
Who will be there?
More than 350 Olympic and Paralympic athletes are due to attend.
Champion heptathlete Jessica Ennis Hill has said that the event will be her farewell to fans as she plans to retire from athletics.
The mayor of London, Sadiq Khan, said: “Our Olympic and Paralympic heroes have inspired millions of people all over the country and I’m incredibly proud of their amazing, record-breaking achievements.
“Over the next few days, the nation will come together to show our gratitude and to celebrate everything our Olympic and Paralympic athletes have achieved.
They deserve nothing less than a real heroes’ return in the heart of the capital and I urge all Londoners to get down to Trafalgar Square on Tuesday to cheer them on.”
More than 150,000 people lined the streets of Manchester despite the rain on Monday evening to welcome home Team GB and ParalympicGB athletes.
Dame Sarah Storey, Max Whitlock, Jade Jones and Nicola Adams were among those in attendance.
Kaiser Chiefs and X Factor star Rebecca Ferguson performed in the city’s Albert Square to the massed crowds, after the parade.