The 24-year-old's last appearance for Italy was in their 20-10 win over the USA Eagles in June having appeared in all five of their 2012 RBS 6 Nations clashes.
And Gloucester director of rugby Nigel Davies revealed D'Apice's international experience and his impressive preseason form with the club were the contributing factors for signing the hooker.
Davies said: "Tommaso has been on trial here for just over a month now. He's an international hooker who has played for Italy in the Six Nations and in the World Cup.
"The big thing for Tommaso is to get the opportunity to play at the highest level in English club rugby. He's a young aspiring player and wants to play for a team that can help to develop his game.
"He's committed a lot to coming here. He could probably have gone to other clubs for a lot more money but wanted to be part of this Gloucester team and we're delighted to have him on board."