The speech was given just metres away from Downing Street and within sight of the Houses of Parliament.
The Tour of Britain finale - soaked in late summer sunshine - was the first major sporting event held in London since the July suicide attacks.
Pointing to a small girl on a bike, Ken Livingstone said he wanted her to grow up thinking cycling in London was a natural thing to do.
He said cycle use had doubled in size in London in the past five years and - to cheers - he said he wanted to see another doubling in size.
Livingstone said he had been enthralled by the professionals who had lapped a one-mile Whitehall circuit 45 times and pledged that Transport for London would continue to support the Tour of Britain. In fact, the support would be increased in years to come.
"We need all the practice we can get in staging major events. If we win [the right to host] the Grand Départ [of the Tour de France] in London, two million people will come here from all over Europe to watch and it will transform perceptions of the sport," he said.
Playing the Olympics 2012 card, he got another cheer when he said London was going to get a world-class Velopark that would leave a lasting legacy for cyclesport in London.
Livingstone's impromptu speech went down extremely well with the crowds, eight deep on some some stretches of the Whitehall circuit, and was applauded loudly by the Tour of Britain organisers.
80 000 spectators lined the one mile circuit, said the Tour of Britain press spokeswoman.
"The turn-out for the race is bigger than last year," said Livingstone.
In a further boost for the Tour of Britain, T-Mobile's Jan Ullrich has said he would like to ride next year's event.
The 1997 Tour de France winner was at Saturday night's Tour of Britain gala dinner celebrating the career of Eddy Merckx.
T-Mobile dominates the Tour of Britain, as a sponsor, as a provider of magenta plastic hands, and as a participating team.
Ullrich said: "I'd really like to do [the Tour of Britain]. I've heard a lot of good stories from my team-mates."
1 Luca Paolini (Ita) Quick Step-Innergetic 1.30.54
2 Enrico Degano (Ita) Barloworld-Valsir
3 Roger Hammond (GBr) Great Britain
ToB CG RESULT
1 Nick Nuyens (Bel) Quick Step-Innergetic 19.04.32
2 Michael Blaudzun (Den) Team CSC 0.08
3 Javier Cherro Molina (Spa) Comunidad Valenciana 0.22
1 T-Mobile 57.04.30
2 Quick Step-Innergetic 8.25
3 Comunidad Valenciana 10.42