Claude Guéant was jailed on Friday for his role in the so-called "Elysée polls" scandal.
The 77-year-old was found guilty of conspiracy and misusing public funds to finance opinion poll contracts worth up to €7.5 million.
The court found that millions of euros billed to the Elysée Palace between 2007 and 2012 had been illegally paid without advertising or competitive bidding.
It is the latest scandal to hit Sarkozy who, although not implicated in this case, has himself been convicted of corruption and irregular campaign financing.
The court ruled that Guéant should spend at least eights months in detention due to his "personality" and the "seriousness" of his actions.
Guéant — who held an "eminent position" — had "consciously violated the rules of public commissioning," judges said. But the former interior minister was acquitted of misusing public funds through negligence.
Guéant, already in jail over a separate offense, will appeal the verdict, his lawyer Philippe Bouchez El Ghozi told AFP.
Three other former close aides to Sarkozy were also sentenced on Friday and are set to appeal.
Patrick Buisson — an adviser to Sarkozy — was given a two-year suspended sentence and fined €150,000. Meanwhile, pollster Pierre Giacometti was given a six-month suspended prison sentence and a fine of €70,000. Both men's companies were also fined.
Emmanuelle Mignon, a former director of the French cabinet, was given a six-month suspended prison sentence, while the polling company Ipsos was also fined €1 million.
The court ruled that the four suspects had committed crimes that "seriously undermined the authority of the state" and "brought the presidency of the French Republic and the senior civil service into disrepute".
The former Sarkozy aide Julien Vaulpré was the only defendant to be cleared in the trial.