Miller, who also played for Celtic, Manchester United, Hibs and QPR, won 21 caps for the Republic of Ireland.
Danny Higginbotham, who played alongside Miller at Sunderland, described the 36-year-old as a “great player but more importantly a fantastic person”. “So sad. Devastating news. My thoughts are with his family,” he wrote on Twitter.
Sunderland paid tribute to the player who made 60 appearances for the club from 2006-2009.
He played an integral role in the promotion as Championship title winners in 2006-07 under Roy Keane, who signed Miller from Manchester United.
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He managed three goals for Sunderland, most notably a ferocious, last-minute strike from just outside the box to rescue a 2-2 draw at Middlesbrough in 2007.
The club tweeted: “We are saddened to hear this evening that former Sunderland midfielder Liam Miller has passed away.
“Our thoughts are with his family and friends at this time.”
Celtic, his first club, said they were “deeply saddened”, adding that their “thoughts are with his family and friends”.