Prince George's County Executive Rushern Baker III signed that county's bill Tuesday morning, the Washington Post reported. Baker called the increase, which would take effect in 2017, "the right thing to do."
The Washington measure still needs a final council vote, expected in January, the Post said. Tuesday's vote was unanimous, suggesting the increase will have no problems passing.
In Washington, the increase would become effective in 2016. The bill also links the minimum wage to inflation.
Montgomery County legislators have also approved the hike.
If the increase takes effect in all three jurisdictions, the city and its two neighbors, with a total population of 2.5 million, would have the highest minimum wage in the country. The federal minimum is now $7.25 an hour.
Baker said he signed the Prince George's bill because of the regional agreement. Without that, he said, he favored letting the Maryland legislature set the wage for the state.