The 23-year-old said: "It was a big wrench for me to leave Motherwell as I had some great years there and the supporters were always fantastic to me.
"But I felt as though a new challenge would do me good and after speaking with the chairman and the manager it's obvious that the club have massive ambitions.
"The new stadium looks brilliant and you get the feeling that Hull City don't want to be hanging around in the third division.
"That's important because I have ambitions of my own and I think that I could achieve a lot of them down here."
Meanwhile as one player joins the ranks at Boothferry Park, another has left. Rob Matthews, who was transfer-listed at the end of the season, has agreed a deal with the club to have his contract paid off.
Matthews joined in May 2001 for £30,000 from Stockport and helped City reach the play-offs, but then couldn't keep his place the following season. The 31-year-old winger scored 4 goals in his 30 games here.