(AFP) - The change is expected to prompt thousands of requests to become German – especially from Turkish people who moved to Germany for work.
"People have now fully taken in that there will be dual citizenship. And many are now applying as quickly as possible."
The law, formally passed in March, comes nearly three years into the reign of the centre-left coalition of Social Democrats, Greens and the Free Democrats.
The reform will bring Germany into line with other European countries such as Italy, Sweden, Ireland and France allowing dual citizenship.
Before the changes, dual citizenship was possible only for European Union and Swiss nationals as well as children in a couple where one of the parents was from abroad.
Israelis and refugees threatened with persecution in their home country were also allowed to hold two passports.
Citizenship 'precious'
The opposition centre-right Christian Democratic Union has argued against any amendments to the laws.
"German citizenship is something very precious, and one should treat it very carefully," CDU leader Friedrich Merz told German broadcaster ARD when the first draft was published in December 2022.
The far-right Alternative fur Deutschland also hit out at the plans, which comes as the National Rally (RN) in France suggests a tightening up of rules on who can enter the country and what dual nationals will be able to do if it gains power in upcoming elections.
"With regard to dual nationals, I can confirm that the state's most strategic positions will be reserved for French citizens and French nationals," said the RN's Jordan Bardella on the election campaign trail.
As well as allowing multiple nationalities, the new laws in Germany will reduce the residency period needed to apply for citizenship from eight to five years.
Some people will be able to apply after three years if they speak German fluently or have excelled in the professional environment.
A special dispensation has also been offered to the "guest worker" generation of Turkish people, who came to Germany in the late 1960s and early 1970s to fill jobs during "Das Wirtschaftswunder" – economic boom.
Anyone in this category will not need to take a formal language or citizenship test.