The Senate Executive Committee passed the legislation Thursday, sending it to the full Senate. It wasn't clear when that vote would take place.
If the measure becomes law, Illinois would become the 10th state to approve same-sex marriage. It would be the first state to adopt it after momentum built following several successes across the nation in the November election and public encouragement from President Barack Obama.
Advocates are pushing for full gay marriage rights just 18 months after the state recognized civil unions.
Many faith organizations are opposed on religious freedom grounds, arguing the proposal would compel them to treat same-sex unions as the equivalent of traditional marriage.