German citizenship is generally acquired automatically by birth according to the principle of descent if one or both of the parents are German. This means you can normally apply directly for a German passport or national ID card for your child.
If only the father is German, there must be a valid acknowledgement of paternity. For children born in the United Kingdom this is generally the case if the father is named on the birth certificate as the “father”, and both parents are named as “informants”.
In the case of German nationals born abroad on or after 1 January 2000, their children, if born abroad, only acquire German citizenship if the parents notify the relevant German mission abroad of the child’s birth within one year.
No, if your child automatically acquired two nationalities by birth (German nationality by descent), from a German perspective he/she will not have to choose between the two nationalities later on. In other words your child has permanent dual national status. However, in some circumstances, the law of the other country may require him/her to choose. In this case please contact the relevant authorities in the other country.
Since 1 January 2021, if you acquire British citizenship by applying for it yourself, without first having obtained permission to retain German citizenship from the Federal Office of Administration (Bundesverwaltungsamt), you automatically lose your German citizenship.
Naturalisation in the German federation is primarily for people who also have their ordinary residence in Germany. Your partner is generally legally entitled to be naturalised once he/she has been living legally in the Federal Republic for three years, subject to certain additional criteria. You have to have been married for at least two years. For further advice, please contact the authority responsible for your place of residence in Germany.
If you and your partner live in the United Kingdom (or another foreign country), naturalisation is only possible if the criteria set out in section 14 of the German Nationality Act (Staatsangehörigkeitsgesetz) are met. However, in the experience of the Federal Foreign Office and the German missions abroad, it is only permitted if – in addition to meeting the application criteria like being able to support yourself financially and possessing good German language skills – your naturalisation would be of particular public interest. Private interests are only a secondary consideration here. As a rule, being married to a German national is not on its own sufficient to demonstrate that naturalisation would be in the public interest.
To avoid submitting a naturalisation application with no prospect of success, for which you will still be charged, it is worth enquiring with the Federal Office of Administration, as the competent citizenship authority, before submitting your application via the diplomatic mission.