Apart from the temporary exclusion I mentioned in a comment, the German "Bundeswahlgesetz" allows to exclude rightfully elected members of parliament at least in two cases:
§ 46 Verlust der Mitgliedschaft im Deutschen Bundestag (1) Ein
Abgeordneter verliert die Mitgliedschaft im Deutschen Bundestag bei
- Ungültigkeit des Erwerbs der Mitgliedschaft,
- Neufeststellung des Wahlergebnisses,
- Wegfall einer Voraussetzung seiner jederzeitigen Wählbarkeit,
- Verzicht,
- Feststellung der Verfassungswidrigkeit der Partei oder der Teilorganisation einer Partei, der er angehört, durch das
Bundesverfassungsgericht nach Artikel 21 Abs. 2 Satz 2 des
Grundgesetzes.
1 and 2 mean that the MP has not been properly elected in the first place (election fraud or changes due to a recount), 4 means he reneges voluntarily. Relevant for the question are 3 and 5.
"Wegfall einer Voraussetzung seiner jederzeitigen Wählbarkeit" means that he would not be eligible in case of a new election. E.g. you cannot be elected if you are a convicted felon, so presumably you would lose your seat (since MPs have immunity the bar for this is very high, and in cases that I can remember they usually stepped down voluntarily).
"Feststellung der Verfassungswidrigkeit der Partei oder der Teilorganisation einer Partei, der er angehört" means that if the party the MP belongs to, or any organisation run by the party, is deemed unconstitutional (in this context, actively seeking to overthrow the constitution), their members can be removed from parliament. Again, the bar for this is very high, the only example I can (vaguely) remember is that in the 1950s some minor extreme right wing organisation was declared unconstitutional and lost their seats (I will see if I find the details, but no promises). This requires a decision by the Verfassungsgericht (broadly equivalent to the US Supreme Court).
After the courts have ruled, this (i.e. expulsion) requires a decision by the Council of Elders of the Bundestag (sounds a lot less Tolkienesk in German), so while not all PMs are involved in the decision, it is a decision made by at least some elected members.
My source for the above is a page by the Federal Agency for Civic Education/Bundeszentrale für Politische Bildung. Unfortunately they only say the the decision has to be made without delay ("Die Entscheidung ist unverzüglich von Amts wegen zu treffen"), but not if the council has much leeway regarding the outcome, or if this is just a confirmation of the court decision.