Antenucci put pen to paper after a day of talks at Elland Road and is now awaiting international clearance ahead of United’s game at Watford this weekend.
Leeds paid an undisclosed fee to make the former Torino forward their 11th signing of the summer, strengthening an attacking line weakened by the loss of Souleymane Doukara to injury.
Doukara will be out for at least a month after rupturing ankle ligaments in Saturday’s 1-0 win over Middlesbrough but Antenucci is in line to make his debut away at Vicarage Road if Leeds secure the necessary paperwork in time.
Writing on Twitter, Antenucci said: “Proud to be part of this club. Hope to give you a lot of satisfaction.”
United have been monitoring Antenucci for the past fortnight and stepped up their interest in him after a £850,000 bid for Rotherham United forward Kieran Agard collapsed.
Agard failed to agree personal terms during negotiations with Leeds last Friday and is now set to join Bristol City in League One.
Antenucci is well travelled in the Italian divisions and has played for Catania, Venezia and a number of lower league sides during a lengthy career.
Leeds, meanwhile, are continuing to press for a deal to sign Adryan, the 20-year-old Brazilian midfielder on loan at Cagliari from Flamengo.
Negotiations over Adryan’s signature look likely to run into next week but United owner Massimo Cellino remains hopeful of securing a player who he described as a “natural number 10.”