In addition there is an open warrant for the arrest of the aide, Brent Furer, in Baton Rouge on a drunken driving charge, ABC News reported Wednesday.
Furer worked on Vitter's last re-election campaign and has worked for the last five years in Vitter's Washington office, ABC said, on matters including women's issues.
One watchdog group says employing someone with Furer's background showed poor judgment by Vitter, who has spoken forcefully as an advocate for women and against drunken driving.
"It says something terrible about Senator Vitter's judgment that this is the kind of guy he wants to keep in his office," Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, said.
Furer's resignation, Sloan said, was "an obvious attempt by the senator to save himself with women voters as heads into his re-election campaign this fall."
"Senator Vitter knowingly kept this dangerous person on his staff through his drunk driving arrest in 2003 and his chilling domestic violence assault conviction in 2008," Sloan said. "Why have him resign only now?"