Byrnes has missed his side's last two matches against the Hurricanes and Cheetahs after he was found guilty of making illegal contact with the eye of Waratahs centre Tom Carter in round two.
But a SANZAR appeal committee chaired by Nicholas Davidson overturned the decision on Thursday on the grounds that there was insufficient evidence to sustain the charge.
"Applying the standard of proof required under the Rules, the appeal committee concluded that it could not be said that a breach of the Laws occurred to the requisite standard as an act of recklessness which involved contact with the eye area," SANZAR said in a statement.
"This was a serious allegation and must be clearly established on the balance of probabilities.
"In the circumstances, the appeal was allowed and the sanction was set aside.
"On appeal it was contended that the citing as originally detailed could not have been upheld on the facts, and the Judicial Officer was wrong to amend the detail of the citing.
"The citing alleged an attack to the eyes as the players were getting up after clearing out.
"The judicial officer considered video footage before the players fell to ground, not as they were getting up and that founded his Decision.
"The appeal committee rejected the submission that the judicial process was confined to the timing alleged in the citing and held there was no unfairness in the process adopted."
The veteran lock is eligible to make his return immediately, however he has not named in the Rebels side to face the Force on Friday night.
Byrnes is expected to begin his comeback against the Highlanders in Dunedin next Friday.