Mullin, who is 32 and arrives on a free-transfer, played for Ronnie Moore when the current Rovers boss managed Rotherham, guiding them to two promotions.
Rovers have also signed Nottingham Forest striker Gareth Taylor on a two-year contract, subject to a medical and Australian Shane Sheriff, subject to a medical and a visa.
Taylor, a striker, has played 12 times for Wales and scored over 100 career goals. Ironically, it was he who scored the winner for Forest against Rovers at the City Ground last season, after coming on as a substitute.
Sheriff, a defender, is a former Leeds United trainee, and over the last three years, the 23-year old has been playing in Denmark for Aarhus. Sheriff was also a member of the Australian Olympic Team in the Athens 2004 games.
Once Sheriff recieves his Visa in Australia, he will travel back to England to undergo a medical with Rovers.