Slater, 22, who spent last season on loan at City, has been widely expected to head back to East Yorkshire for several weeks, with the move due to have been completed earlier this week.
The Sheffield-born player - who was high on the wanted list of former Hull head coach Grant McCall from back in the summer - has now completed his switch to Hull and has become the first signing of the Acun Ilicali era, with new head coach Shota Arveladze set to be officially unveiled in front of the media at a press conference on Friday lunch-time.
Slater has joined for an undisclosed fee after agreeing a two-and-a-half-year contract, with a club option of a further year.
On finally sealing his switch to Hull, a relieved Slater said: “It’s definitely a good feeling (to be here). I’d been waiting on it since the summer. This is where I wanted to be and I’m delighted to be back.
"Last season, I worked towards getting Hull to the Championship and I feel like I deserve my shot at seeing what I can do (at this level). I’m excited to jump in.
“I’m ready to kick on with my career. I want to be playing games and I couldn’t think of a better place to do it. I want to test myself in the Championship. I believe I can do it and I want to prove that now.
“I can’t wait to meet the fans – we missed out massively last season not having the fans with us and sharing the journey we went on.
“If we can make some more memories, that’d be a lovely touch.”
On Wednesday, Hull were given the green light to instigate some key transfer business after confirming that they are no longer working under transfer restrictions after repaying an EFL-monitored loan.
The Tigers have also been linked with a number of players based in Turkey including Fenerbahce's Iranian frontman Allayhar Sayyadmanesh and ex-Liverpool attacker Ryan Babel having been linked.