Dunn made his England debut against Portugal in September 2002 but was sold to Birmingham in July 2003 by the Rovers boss Graeme Souness, who criticised his lifestyle.
After an injury-plagued time at Brum, Rovers snapped him up for a cut-price £2.2million in January.
Dunn said: "A lot of people say never go back to where you've been successful but I'm more mature now as a person and a player."
Dunn added: "When I met the gaffer he just said ‘Well I went back to United' and everyone knows what happened there.
"That changed my mind a little and I'm glad I made the move."