The 27-year-old signed a three-year deal this week after joining from Preston for an undisclosed fee.
Despite interest from Premier League sides, the former England u-21 international chose Elland Road.
Lonergan told the club website: "This is a massive football club that wants to get to the Premier League. I want to get to the Premier League here."
He added: "It wasn't a big decision football-wise, but it was family-wise. But as soon as I heard of the interest, which was probably six weeks ago, I knew where I wanted to go."
Lonergan is set to make his debut in a Leeds United XI at Bradford Park Avenue on Wednesday.