Sheehan joined on a two-year contract in June 2011 after leaving Swindon Town.
The left-back quickly became a fans’ favourite with his dangerous set-piece deliveries that contributed to his 10 assists and three goals during 2011.12.
A product of Irish outfit Belvedere FC, who have brought through the likes of former loanee Brendan Moloney and Fulham's Stephen Kelly, Sheehan was brought to England by Leicester City.
The defender represented the Republic of Ireland national team at under-19 and 21 levels during his five-year stay at the Walker's Stadium.
Following a successful loan spell, Sheehan later made the switch to Swindon Town, where he spent one season prior to linking up with the Magpies.