Holder told ABC's Pierre Thomas in an interview that has yet to air that he expects the Justice Department to join lawsuits challenging laws in both Ohio and Wisconsin.
GOP lawmakers in the Buckeye State passed measures earlier this year that chopped six days off the state's early voting period, while Ohio Secretary of State Jon Husted eliminated early voting on Sundays.
A federal judge in Columbus, Ohio ruled last month that the state must restore three days of in-person early voting, although other restrictions remain in place.
In February, a voter ID measure in Wisconsin was also struck down by a federal judge.
The litigation in each state remains ongoing, and Holder said the Justice Department is ready to intervene.
“I expect that we are going to be filing in cases that are already in existence in Wisconsin as well as in Ohio,” Holder said, as quoted by MSNBC. The interview was conducted Friday in London, where Holder was attending meetings about terrorism threats.