This should come as no surprise to anyone, but the PC version of Watch Dogs will require the use of Ubisoft's Uplay service.

This news was confirmed by an Ubisoft representative speaking with IGN.
"Like some of our other AAA releases, including Far Cry 3, Splinter Cell Blacklist, and Assassin's Creed IV Black Flag, Watch Dogs will be available on Steam and will leverage Uplay to support the games services."

This comes just a few days after it was revealed that the PC version of the game will require an eight core (virtual or physical) CPU for its recommended specs.