In 1964 he moved with his second wifeto New York and was able to continue his success with numerous exhibitions. Likewise, many of his works have developed there, ranging from photorealism to pop art and geometric abstraction.
After the failure of his second marriage Seidel fell into a strong depression from which he should never fully recover. At the age of only 47 he commit sucide in 1971. A large part of his estate was shown in 1992 in a retrospective at the Staatliche Kunsthalle Berlin, the Hallerschen Kunstverein and in Cologne.