The state's Senate Judicial Proceedings Committee heard testimony from supporters and opponents of the legislation last week.
Baltimore County Sen. James Brochin (D) said his position changed after he listened to the seven-hour hearing. He said he felt "appalled and disgusted" by the comments made by opponents of the same-sex marriage bill.
The bill needs 24 votes to pass on the floor.
In the past, the strong influence of socially conservative groups like the Catholic Church and some African-American congregations has stopped the state from moving forward on gay marriage.