Basso, no relation to former Giro d'Italia winner Ivan Basso, brings the average age to 27.5, with other young newcomers Egan Bernal, Pavel Sivakov, Kristoffer Halvorsen, and Chris Lawless.
"It's a dream come true to be joining Team Sky," Basso said. "My main objective is to help the team wherever I can. I want to learn about the job and what it means to be a pro bike rider. I want to learn as much as I can from my teammates and increase my level day by day."
Basso previously rode as a trainee for the Trek-Segafredo squad in 2015, taking third at a stage in the USA Pro Challenge from a breakaway.
Directeur sportif Dario Cioni describes Basso as a sprinter "who can survive the punchy climbs and he has the speed to sprint from smaller groups," and said his signing was based on the results over the past few years.
"We're happy to see Leonardo turn pro with us next year. He's got potential and we want to see where we can get to working together," Cioni said.
With the exit of more experienced riders like Elia Viviani, Danny van Poppel, Peter Kennaugh, Mikel Nieve and Mikel Landa, the team is putting more of a focus on young riders, despite also signing Jonathan Castroviejo, David de la Cruz and Dylan van Baarle.
Team principal Dave Brailsford explained, "We are establishing a group of exceptional young riders at Team Sky. I have no doubt they are going to make a big impact and be an important part of our future.
"I believe the group of home grown and international young talent we are building represents the brightest future we have ever had at Team Sky."
2018 Team Sky rider roster:
Leonardo Basso – Italy – age 23
Egan Bernal – Colombia – age 20
Jonathan Castroviejo – Spain – age 30
David de la Cruz – Spain – age 28
Philip Deignan – Ireland – age 34
Jon Dibben – Great Britain – age 23
Owain Doull – Great Britain – age 24
Kenny Elissonde – France – age 26
Chris Froome – Great Britain – age 32
Tao Geoghegan Hart – Great Britain – age 22
Michal Golas – Poland – age 33
Kristoffer Halvorsen – Norway – age 21
Sebastian Henao – Colombia – age 24
Sergio Henao – Colombia – age 29
Benat Intxausti – Spain – age 31
Vasil Kiryienka – Belarus – age 36
Christian Knees – Germany – age 36
Michal Kwiatkowski – Poland – age 27
Chris Lawless – Great Britain – age 22
David Lopez – Spain – age 36
Gianni Moscon – Italy – age 23
Wout Poels – Holland – age 30
Salvatore Puccio – Italy – age 28
Diego Rosa – Italy – age 28
Luke Rowe – Great Britain – age 27
Pavel Sivakov – Russia – age 20
Ian Stannard – Great Britain – age 30
Geraint Thomas – Great Britain – age 31
Dylan van Baarle – Holland – age 25
Lukasz Wisniowski – Poland – age 25