He is currently under investigation for possession of child pornography he said he downloaded as part of his work against the trade in such images.
He left the Social Democratic Party (SPD) over the weekend in protest at its decision to support a bill giving the government the power to censor websites containing child porn.
The Pirate Party in Germany sees itself as representing those in the information technology community, campaigning for privacy protection as well as the loosening of copyright laws.
Although Tauss is known for his experience in information technology matters and he has a track record in investigating child porn websites, he said the decision to give the government powers to close such sites down is a mistake.
He released a statement on Friday explaining his departure from the SPD, saying that although he agreed with many points of the party's programme, there was a “terrible wrong turn being taken” in domestic, legal and internet policy.
He promised to continue to vote with the SPD in matters unrelated to these topics, but the party has demanded he step down from his parliamentary seat.
“We have to acknowledge this step [that he has left the party] and call on him to give back his parliamentary mandate,” said SPD Baden-Württemberg party head Ute Vogt at the weekend.
Christian Lange, spokesman for MPs from the state told the Welt am Sonntag newspaper, “It is not on to capture the parliamentary mandate. He got it through the SPD and therefore has to give it back.”
The Pirate Party welcomed Tauss into its ranks, saying that as long as the investigation into his possession of child porn images did not result in a conviction, there was, “no reason to doubt his innocence and moral integrity.”