The England elite squad member is suspended until November 1 following an RFU hearing at a Heathrow Airport hotel, English rugby's governing body announced. The ban runs from March 22.
Clark, 22, was cited after an incident during Northampton's LV= Cup final defeat against Leicester 11 days ago, and then suspended indefinitely by his club.
Clark, who captained Saints in the final, was reported for an act contrary to good sportsmanship, allegedly hyperextending Leicester hooker Rob Hawkins' right arm.
It left Hawkins with a broken elbow and requiring surgery, sidelining him for the rest of this season.
In a statement the RFU said: "Calum Clark of Northampton Saints was this evening suspended for 32 weeks for an act contrary to good sportsmanship - Law 10(4) (M).
"Clark pleaded guilty to hyperextending the right arm of Leicester Tigers' Rob Hawkins during the LV= Cup final at Sixways on March 18.
"The suspension will run from March 22 to the November 1. He is free to play again on November 2 2012.
"Clark is ordered to pay hearing costs of £500.
"The full judgement will be made available tomorrow [Friday]. The player has the right to appeal."
Clark is the second Northampton forward to receive a lengthy ban this week after club skipper and England hooker Dylan Hartley landed an eight-week suspension for biting Ireland flanker Stephen Ferris' finger during an RBS 6 Nations game on March 17.
Hartley will be available for England's three-Test summer tour to South Africa and the Aviva Premiership final at Twickenham on May 26, should play-off contenders Saints get there.
But Clark faces a far longer period of time in which to contemplate his actions that left an opposition player seriously injured.
A former England Under-20 skipper who joined Northampton from Leeds Carnegie, Clark is viewed among a promising array of young back-row talent currently available to newly-appointed England head coach Stuart Lancaster.
But an RFU panel, chaired by the organisation's disciplinary officer Judge Jeff Blackett, left Clark knowing in no uncertain terms how his behaviour in the LV= Cup final has been viewed.
Clark's suspension of more than seven months is among the longest handed out to a senior English player during rugby union's 16-and-a-half-year professional era.
But television footage of the incident at Sixways could have left few people in any doubt about its severity.
And Northampton, fourth in the Premiership ahead of Saturday's trip to Bath, now find themselves without two key players for the regular league season climax that also sees them host Leicester, visit Exeter and then entertain Worcester.
Northampton's suspension of their player followed an internal investigation at Franklin's Gardens and was a clear pre-emptive strike prior to tonight's hearing.
Television pictures showed former Bath forward Hawkins reeling away in agony from a 21st-minute ruck.
It was an incident that enraged Leicester rugby director Richard Cockerill.
"If Clark is deemed to have done it on purpose it's pretty horrendous," Cockerill told BBC Radio Leicester after the final.
"Something has gone on there, but we will let them look at it and sort it out. It's a pretty poor act. I think it is really out of order and in my opinion it's as bad an injury as I've seen on a rugby field."
Clark's rugby career is now on hold, with any international ambitions he might have held lying in cold storage.
He cannot return to playing until eight days before England's opening autumn Test against Fiji, but with an updated elite player squad due to be announced in July, he could easily be dumped from international contention.