Williams was cited after it appeared that his boot had made contact with the head of Lewsey at a ruck in the 75th minute of the match.
The incident was caught by the TV cameras, but not by Australian referee Stuart Dickinson or Irish touch judge Alan Lewis, who was in close attendance. A penalty was awarded against England at the same ruck.
The Judicial Committee met on Sunday to consider the charge against Williams, after he was cited by citing commissioner Michael Somes (Australia).
Williams pleaded not guilty to the incident.
The judicial committee, in its finding, determined that the contact with the English player's head was inadvertent and incidental to Williams' endeavour to ruck the ball in a situation where access to it was impeded by the position of the English players in the ruck.
The Judicial Committee found that the offence was not proven and no further action was taken.
The Judicial Committee was chaired by Michael Goodwin (Australia) with Bruce Squire, QC (New Zealand) and Mattie Blackburn (New Zealand) also on the panel.
England fans will not be happy with the outcome, after their team fell foul of Dickinson during the match, with back rowers Neil Back and Lawrence Dallaglio both being sin-binned in the early stages of the second half for killing the ball at the ruck.