Cadman will lead the agency with Publicis USA chief creative officer Bob Moore, who is based there.
He replaces Randy Browning, who left the agency in March to pursue other opportunities.
Cadman left Euro RSCG London in December last year after what agency sources termed "a difference of opinion over the future direction of the agency". Russ Lidstone was appointed as his successor in May.
Cadman said: "I am thrilled to be joining the Seattle office of Publicis, one of the most exciting creative agencies in the US. Having Bob Moore there to partner with in Seattle is a huge opportunity for me to do what I love - to lead a truly creatively driven agency."