Gov. Charlie Baker signed a $261.1 million fiscal 2021 supplemental budget bill that revives mail-in and expanded in-person early voting through Dec. 15 and establishes a new MBTA board of directors.

Baker signed the bill (H 3973) on Thursday in full, approving all spending items and outside sections in the budget sent to him last Wednesday.

While the bottom line includes spending that will be reimbursed by the federal government, the bill carries a net cost of $64 million to the state and includes $29 million for COVID-19 response expenses, such as the call-up of the National Guard, and appropriations tied to the 2020 policing reform law.

Five million dollars will go toward funding the new Peace Officer Standards and Training Commission, and an additional $12.5 million will go toward implementing policing reforms in fiscal 2021 and fiscal 2022.

The new seven-member MBTA board replaces the defunct Fiscal and Management Control Board. It will be composed of the MassDOT secretary, an appointee of the T advisory board who has municipal government experience, and five appointees named by the governor -- one with safety experience, one from a transit operations background, one with experience in the finance world, one T rider from an environmental justice population, and a selection from a Massachusetts AFL-CIO shortlist.

Baker's approval of the mail-in voting extension means that voters in municipal elections this summer and fall, including Boston's mayoral race, will be able to utilize the coronavirus-era election reforms.

Boston's preliminary election is set for Sept. 14. The winners of the preliminary will face off in the final election on Nov. 2.