Multiple sources told CNN that Panetta will make the announcement tomorrow.
The move would overturn a 1994 rule banning women from being assigned to smaller ground combat units, according to the AP.
It will give the military until January 2016 to seek any exceptions to the rule.
Four servicewomen along with the American Civil Liberties Union sued the Pentagon in November over the combat ban, calling it unconstitutional, National Public Radio reported.
In February 2012, Panetta relaxed the rules on women serving with combat units, The Hill reported.
Though women were still banned from serving directly on the frontlines, they were now permitted to serve in non-infantry battalion jobs, in positions such as radio operators, intelligence analysts, medics, radar operators and tank mechanics.
They were also permitted to work in closer proximity to combat on the ground.
Women currently comprise 14 percent of the 1.4 million active US military personnel, according to the AP.