The individuals, who included an elderly woman, a mechanic, a pub landlady, and a young mother with her child, were paid expenses and were all reading from a script, Labour confirmed.
Mr Livingstone was pictured wiping away tears as he watched the video at his official manifesto launch on Wednesday. But he had already seen the broadcast once before.
The veteran Labour candidate, who is standing against Boris Johnson for Mayor of London, was mocked last night after the details emerged.
Some of his political opponents speculated privately that Mr Livingstone’s display was “a stunt”.
The disclosures could also rebound on Ed Miliband, who described the video as “very powerful” and was seen to comfort the 66-year-old Mr Livingstone by placing a hand on his back.
The claim raised questions about why the preview raised such strong emotions in Livingstone if the participants lined up to highlight why they wanted him back in city hall were only acting.
Livingstone explained after the broadcast at his election manifesto launch on Wednesday that he had wept because the advert was "a tear-jerker". He said it represented the views of "hundreds of thousands of Londoners who desperately want a mayor who is going to make their life easier in this city".
On Friday, the campaign team insisted that those who took part were genuine supporters recruited by an advertising agency, BETC London. It confirmed their words were scripted, with some participants receiving expenses for taking part. One was a former Labour councillor.
A spokeswoman for Livingstone said: "Everyone who appears in Labour's party political broadcast are ordinary Londoners who are backing Ken on 3 May. No actors were used in the broadcast."
BETC London did not return calls for comment.
Commentators expressed surprise that the advert had been scripted. Dan Hodges, editor of LabourUncut, tweeted: "Ken writes a script in which people are told to say how much they want him to be mayor, then cries at them saying it. And I'm indulgent."
It ends a difficult week for the Livingstone campaign, with Conservative rival Boris Johnson enjoying a six-percentage point lead in the latest ComRes poll, published this week – a wider gap than in a ComRes poll in January, though smaller than the eight-point lead Johnson enjoyed in a separate YouGov poll last month.
The ratings are widely seen as indicative of the damage caused to his campaign by allegations that he benefited from lower tax rates by using a company, Silveta Ltd, to channel his media earnings.
Livingstone had hoped that a joint agreement by four mayoral candidates to publish their earnings and paid taxes last week would draw a line under the issue. But it has refused to go away and he was booed and heckled at a mayoral debate on Wednesday.
Despite agreeing on BBC Newsnight last week that he would publish his earnings and taxes, Livingstone prompted further criticism by releasing only a summary financial statement relating to the income he had taken out of, rather than channelled into, his company, and attendant taxes paid.
One figure omitted was the £70,000 "relocation grant" – effectively his redundancy pay for losing office in 2008 – which was paid directly to Livingstone, rather than channelled through his company.