The LEAFA Premier League leaders announced on Tuesday night that the 35-year-old had joined the Muirhouse-based club.
A post on the club’s Twitter account read: “The one the fans have all been waiting on. The local hero returns home. Still the 3rd all time SPL goalscorer.
“Former Scotland internationalist. Hibs legend. Derek Riordan signs for the Saints!!”
St Bernard’s are the 11th club of Riordan’s career, and are linked to the former Scottish League side of the same name that played in Edinburgh between 1874 and 1943.
The former Hibs striker turned out for Edinburgh City during the second half of last season, scoring three goals in eight games.
Riordan began his career with Hibs, joining the club in 1999 and making his senior debut in 2001 in an Edinburgh derby against Hearts.
After a short loan spell at Cowdenbeath he became a regular fixture in the first team squad, scoring 64 goals in 146 games for the club before signing for Celtic in 2006.
He returned to Easter Road in 2008, and played a further 114 games for Hibs, netting 40 goals in his second spell.
He was capped three times by Scotland between 2005 and 2009, and made ten appearances in total at Under-19 and Under-21 level.
He left Hibs in 2011, initially signing for Chinese side Shaanxi Chanba before brief spells with St Johnstone, Bristol Rovers, Alloa, East Fife and York, before his stint at City last year.