Team Sky's Thomas triumphed in the five-day race, previously known as the Giro del Trentino, to take one of the biggest wins of his career and is the first Briton to win the event.
The 30-year-old Welshman is slated to lead Team Sky, along with Spain's Mikel Landa, at the Giro, which begins on May 5 on Sardinia and finishes in Milan on May 28.
France's Thibaut Pinot (FDJ) won Friday's fifth stage, the 199-kilometres from Smarano to Trento, but had to settle for second overall, seven seconds behind Thomas, who was third on the day.
It was Team Sky's third successive overall victory in the race after Richie Porte's 2015 win and Landa's triumph last year.
Read the original article on Eurosport: Team Sky's Geraint Thomas wins Tour of the Alps, becomes first Brit to do so