The fullback has joined from newly relegated Leicester and will be looking to continue the progress made on his loan spell last season
A former trainee with Leicester City, Sheehan made his first-team debut for the final game of the 2004-05 season against Plymouth Argyle.
A quick, attack-minded left-back and also something of a free-kick specialist, he failed to build on his progress and later spent a loan spell at Mansfield Town. He finally broke into the Foxes side on a regular basis at the start of 2007-08, only to join Leeds on loan in January 2008.
With his Foxes contract having run out, he switched to Elland Road on a permanent basis in July 2008. Alan made his debut for the Eire U21 side against Israel in June 2005.