The Wire actor was previously rumoured to be joining the AMC zombie drama, but his contract has now been confirmed by TVLine.
Coleman will portray Tyreese, a popular character from the original comics who was originally introduced in issue #7.
In the comics, Tyreese became Rick's (Andrew Lincoln) second-in-command following the death of Shane.
The character is rumoured to make his first appearance in the current third season's eighth episode when Rick's camp prepare to fight The Governor (David Morrissey).
Chad Coleman most famously portrayed Dennis 'Cutty' Wise in HBO's The Wire, and has since appeared in the likes of The Good Wife, Burn Notice and I Hate My Teenage Daughter.
The Walking Dead airs on AMC in the US and on FX in the UK.