Seiffert studied at the Musikhochschule in Düsseldorf and made his debut in 1978 at the Deutschen Oper am Rhein, Düsseldorf/Duisburg. In 1979, he was awarded second place in the Deutscher Musikwettbewerb (German Music Competition), and appeared on the TV show Anneliese Rothenberger gibt sich die Ehre (Anneliese Rothenberger has the honour [of meeting ...]).
In 1986, he married the soprano Lucia Popp, 15 years his senior. She died in 1993, after which he married another soprano, Petra-Maria Schnitzer.
He established his career at the Bayreuth Festival, regularly appearing in the title role of Lohengrin, which he last performed in 2005 with his wife Schnitzer in the role of Elsa. In 2003 he was awarded the Grammy Award for Best Opera Recording, for his performance of Tannhäuser, under Daniel Barenboim. Today, he is a sought-after Heldentenor, singing many of the title roles of Wagner's best-known operas.
Most of the information in this article is taken from the German Wikipedia article.