He played in Southend's friendly with Eastbourne on Saturday and will now join former manager Paul Sturrock.
The defender joined Barnsley in 1999 from non-league side Alfreton Town and went on to feature 139 times while at Oakwell.
Cardiff paid around £500,000 for his services in July 2002 and he went on to play 170 games for the Welsh side in a five-year spell that included loan moves to Stoke and Colchester.
A permanent switch to Queens Park Rangers was followed by his stint at Home Park.
Southend have also confirmed a deal to bring Josh Simpson from Peterborough United on loan for six months will be completed as soon as they can register players.
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