The 30-year-old, who had been heavily linked with a move to West Yorkshire for some time, becomes United’s 11th new addition of the summer and their seventh from Italian football.
Antenucci was co-owned by Catania and found himself loaned out to Ternana last season, where he was made captain and hit an impressive 19 goals in 40 appearances for the Serie B side.
The striker’s career has largely been spent below the top-tier in Italy, starting at Giulianova before spells at Ancona, Catania, Venezia, Pisa, Ascoli, Torino, Catania again and Spezia.
Subject to international clearance, Antenucci could make his Leeds debut on Saturday when David Hockaday's side travel to Vicarage Road to face Watford in the Championship.
He posted on his personal Twitter account: "Proud to be a part of this club. I hope to give you a lot of satisfaction."
Leeds have already bolstered their attacking options with the arrivals of Souleymane Doukara, Billy Sharp and Nicky Ajose, but they had been in the hunt for further additions as a move for Rotherham’s Kieran Agard collapsed last week.