And on Tuesday night, in an ABC7 Eyewitness News exclusive, he says the social changes leading to the event are part of a successful journey.
The law will make Illinois the 16th state to legalize same sex marriage.
The signing takes place Wednesday afternoon at the UIC Forum.
"I think this is great progress for our state and for our society and I think it will be looked upon that way in history," said Gov. Pat Quinn.
The bill will be signed on a desk brought from Springfield and once used by Abraham Lincoln.