The Terriers fought off stiff competition from Swindon for the 20-year-old.
Robinson found first-team opportunities limited at Vicarage Road and made just six appearances for the Hornets, but he enjoyed an impressive loan spell at Southend last term, hitting seven goals in 21 games.
He has signed a three-year deal with the West Yorkshire club.
Robinson told Huddersfield's official website: "When I heard of Huddersfield's interest it presented me with an opportunity that I had to take.
"I want to play regularly and I believe that the club can progress to the Championship, which I want to be a part of.
"I believe I'm good enough to play in the Championship, but I never got the chance I thought I should have at Watford. Huddersfield is a big club with a genuine ambition to play in that division, which is where I want to be."