Bortolami was made Italy's youngest captain in 2003 when he led the Azzurri into battle against the All Blacks, following his debut as a 20-year-old.
He has since won 45 international caps and was the fulcrum of an outstanding Italian effort in the second round of the Six Nations Championship against England in Rome earlier this month.
Speaking exclusively to www.gloucesterrugby.co.uk, Bortolami said: "I'm delighted to be joining Gloucester and am looking forward to the challenge of playing club rugby in England.
"There were a number of clubs who expressed an interest in signing me, but I was extremely impressed when I met Dean Ryan and he outlined his vision for Gloucester Rugby.
"The club has a very strong squad, quality coaching staff and excellent training facilities. I have also heard much about the passionate and loyal group of supporters at Kingsholm.
"All the ingredients are there for long-term success - I am keen to play a central role in it."
Ryan, who has already secured the services of a vast number of players ahead of next season could not conceal his delight at Bortolami's arrival and added: ""He is a top quality second row, an outstanding prospect, who could potentially become world class.
"He has been having a storming Six Nations, is 25-years-old and is his national captain - to sign someone of his ability is fantastic for us.
"A lot of clubs were very interested in him but he opted to join us. We wanted more quality in the second row and he is the right option. Sometimes, when we are without Alex Brown, we lack a bit of expertise but Marco will give us that.
"They are pretty similar players, he is a top quality athlete and a lot of people were in the race for him.
"He is a major addition to our squad. I believe we only need two or three top quality players each season to compliment what we already have and Marco is certainly one of those."