The Senate gave its support to all 40 articles of the reform bill, which will also see the number of members cut from 315 to 100, Ansa reported.
Meanwhile, the upper house of parliament will be stripped of most of its powers, a moved aimed at stopping bills getting bogged down in a back-and-forth between the lower and upper chambers.
It would also help prevent a repeat of the political deadlock which followed last year's election, by throwing out rules that make it difficult for any one party to secure an overall majority in both houses.
Late last month, Renzi implemented a so-called bear trap mechanism, which granted MPs 135 hours of debate on Senate reform and required an agreement be reached by August 8th, ahead of the summer recess.
A final vote will take place on Friday morning.