Hartley will be available for the summer tour to South Africa but will only play for Northampton again this season if they reach the Aviva Premiership final on May 26. The 26-year-old was punished by an independent Six Nations committee for biting the finger of flanker Stephen Ferris during the 30-9 RBS 6 Nations victory over Ireland on March 17.
It had been speculated that he would face a lengthy spell on the sidelines having served a 26-week ban for gouging in 2007. But the hearing decided a four-week reduction to eight weeks was appropriate, with Hartley saying: "I am disappointed by the result and I will wait for the written judgment as to how the panel came to their conclusion."
He added: "I now have to put it behind me and focus on supporting Saints in training and off the field."
The written judgment is expected to be published by Friday.
Hartley was accompanied to the hearing by Graham Rowntree, the England forwards coach who is pleased that the Saints will skipper will be able to participate in the summer tour to South Africa.
"It's unfortunate for Dylan and Northampton, especially as he was in good form during the Six Nations and he has developed as a player and a leader," Rowntree said. "However, we are looking forward to him being available for the tour to South Africa."
The offence was found to have contravened IRB Law 10.4(m) "acts contrary to good sportsmanship".
The hearing examined the evidence and listened to Hartley, his legal representative, Northampton director of rugby Jim Mallinder, Rowntree and Ferris via a video link.
It was decided that the offence merited a low entry point in the International Rugby Board's table of sanctions and allowed mitigation of four weeks. The 26-year-old can resume playing from May 14.