The disciplinary committee, which was chaired by Robert Williams (Wales) and also included Mike Hamlin and John Doubleday (both England), upheld the citing complaint and determined that the offending warranted a red card.
In applying the sanction, the disciplinary committee considered that the stamp, contrary to law 10.4(b), was in the mid range of the IRB's sanctions for the type of offence.
After hearing from O'Driscoll and his representatives, the disciplinary committee allowed a reduction of two weeks of mitigation, particularly taking into account the player's exemplary previous playing and disciplinary record.
O'Driscoll is suspended until April 8 and has the right of appeal.
The three-week suspension rules him out of Leinster's next three matches, including the Amlin Challenge Cup quarter-final against London Wasps on Friday, April 5.