Baltimore Cardinal Edwin O'Brien has vowed to overturn Maryland's gay marriage law.

With the help of a single Republican, Senator Allan Kittleman, Democratic senators approved the bill during an evening session on Thursday. Governor Martin O'Malley has said he will sign the bill into law, which would make Maryland the eighth state to legalize gay marriage.

This was the second time the chamber has approved the measure. A gay marriage bill cleared the Senate last year before it was ultimately shelved in the House of Delegates due to lack of support.

The House joined the Senate last week in approving marriage equality.

“Though not a surprise, today's vote to redefine marriage in the State of Maryland by some members of the State Senate, is no less troubling for it places Maryland one step closer to the dismantling of the most fundamental social institution in all of society,” O'Brien said in a statement released on Thursday.

“The Catholic Church, like others throughout western civilization for thousands of years, has regarded marriage for its unique gifts rooted in nature, and respected that only God alone – not the Church and not government – bestows the true meaning upon this relationship that He created.”

“Now, Maryland's politicians unconscionably have chosen political expediency over the good of society – the fundamental charge of their office – by daring to redefine this sacred union between one man and one woman. Their action poses a grave threat to the future stability of the nuclear family and the society it anchors. The Archdiocese will continue to advocate for the preservation of both and will eagerly and zealously engage its 500,000 members in overturning this radical legislation, and will join with the hundreds of thousands of others in this Archdiocese and throughout Maryland in aggressively protecting the God-given institution of marriage.”

O'Brien also offered a prayer.

“Let the light of Thy divine wisdom direct the deliberations of Congress, and shine forth in all the proceedings and laws framed for our rule and government, so that they may tend to the preservation of peace, the promotion of national happiness, the increase of industry, sobriety, and useful knowledge; and may perpetuate to us the blessing of equal liberty.”