Simmons, on as a replacement at the Stade de France, was cited for a tip tackle on Nyanga in the second half of the match won 33-6 by France earlier this month.
The reduced punishment rules Simmons out of the Wallabies' last match on their tour of Europe against Wales after he missed the matches against Italy and England.
The Six Nations Committee said in a statement that the player will be free to play from February 4.
"The appeal committee ... found that the player's offending had merited a mid-range entry point, rather than the top end entry point that the Judicial Officer had originally found," they said.
"After applying aggravating and mitigating factors, the appeal committee imposed a reduced sanction of five weeks."
The Wallabies will travel to Cardiff looking to make it three straight Test wins after victories over Italy and England following the defeat by France.
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