Hartley had been cited for striking prop Rabah Slimani in the 30th minute of last Saturday’s Champions Cup defeat to Clermont Auvergne at Stade Marcel Michelin.
He had been shown a yellow card by referee Ben Whitehouse following the incident, which was later flagged up by match citing commissioner Douglas Hunter.
That meant Hartley faced a hearing in London, with the independent disciplinary committee receiving evidence and submissions from Hartley, who pleaded not guilty to the charge, Saints’ legal representative, Sam Jones, and director of rugby Jim Mallinder.
The committee also heard evidence and submissions from the EPCR disciplinary officer Liam McTiernan.
The committee found that Hartley had committed a reckless act of foul play in that he had struck Slimani in the face, but the committee was not satisfied that the offence had warranted a red card.
The citing complaint was therefore dismissed and Hartley is free to play in this weekend’s Aviva Premiership match at Franklin’s Gardens.