Italy's Senate adopted a "super amendment" on Thursday to gay union legislation, paving the way for the contested bill to become law.
A final vote on the full text of the draft law in the Chamber of Deputies is seen as a formality and is expected within two months.
Italy is the last major country in western Europe not to offer gay civil unions, with close ties to the Vatican sinking all previous attempts.
The "super amendment" removes from the draft text rights for same-sex pairs to adopt stepchildren and a requirement that couples be faithful.
Prime Minister Matteo Renzi's centre-left Democratic Party failed to push through a more robust version of the bill last week, after the opposition Five Star Movement (M5S) withdrew its support at the last minute.