Senate President M. Teresa Paiva Weed proclaimed it "a historic day" after the 21-16 vote in favor of a bill legalizing civil unions, The Providence Journal reported.
Gov. Lincoln Chafee said Wednesday he would sign the bill, which already has House approval, if it passed in the Senate.
Rhode Island joins a small but growing number of states affording gay couples civil unions designed to be provide rights similar to those afforded heterosexual couples, but not marriage.
The bill had drawn fierce opposition on both moral and religious grounds, while some lawmakers called approval of the measure a step toward equality.
The vote came 2 hours after the Senate Judiciary Committee voted 7-4 to recommend passage of the bill.
Paiva Weed, who voted for the bill, called it "a compromise" and "a vote for equality."
"From hospital visitation rights, medical decision-making powers, equal state tax treatment, we have moved one step in the right direction to ensuring that individuals receive equal rights and protections under the law," she said in a statement.