Claude Guéant, considered one of Sarkozy’s closest confidants, went on trial in October along with four other aides and allies over accusations they misused public money while ordering public opinion polls worth a combined €7.5 million.
Guéant, who is already in jail over a separate offence, was handed a one-year prison sentence by a court in Paris on Friday, with a requirement to serve a minimum of eight months.
Writer and one-time Sarkozy advisor Patrick Buisson was handed a two-year suspended sentence and a €150,000 fine, while former cabinet director Emmanuelle Mignon was given a six-month suspended sentence.
Former pollster and consultant Pierre Giacometti was also convicted and handed a six-month suspended sentence and a fine of €70,000.
They were accused of ordering polls for Sarkozy in secret and without competition, breaking French laws on public financing that require transparency and competitive bidding.
Former Sarkozy aide Julien Vaulpré was the only one of the five accused to be cleared.
Sarkozy was not targeted directly and had refused to testify as a witness until compelled to do so by a judge.
In September last year, a separate court handed Sarkozy a one-year prison sentence for illegal financing of his 2012 re-election bid, seven months after he received a jail term for corruption.
The 66-year-old, who is appealing both of those convictions, has also been charged over suspicions he received millions of euros for his 2007 election campaign from the late Libyan dictator Muammar Kadhafi.
Guéant, 77, was jailed in December after he was found to have failed to pay a fine and damages to the state relating to a previous sentence, handed down in 2017, for operating a suspected slush fund.
He immediately announced an appeal against Friday’s sentence.