Germany’s anti-immigration, rightwing populist Alternative für Deutschland is preparing to play a noisy role inside the country’s next parliament, after a coalition deal between Angela Merkel’s CDU and the SPD was announced on Wednesday.

The renewed grand coalition – which is subject to a vote by the SPD membership – puts the two largest parties on to the government benches and makes the AfD, the third-placed party in September’s federal elections with 92 out of 631 Bundestag seats, the main opposition.

AfD leader Alexander Gauland was quick to lay into the coalition agreement on Wednesday, arguing that the negotiations had left Merkel’s conservatives an empty shell. “The CDU has given up as a party so that a Merkel without any real content can stay at the top thanks to Social Democrat support,” he said.

Germany’s system of proportional representation will not assign the AfD an official status as the leading opposition party, but parliamentary tradition decrees that it can lay claim to a number of privileges that other parties will struggle to deny it.

Whenever Merkel makes a statement in the Bundestag, the AfD will be the first party allowed to respond – a running order that is usually replicated in TV reports on parliamentary debates. On budget debates, the AfD will get to speak ahead of the government.

The first overtly nationalist party to enter the German parliament in half a century has already taken over a number of formal traditions usually handed to opposition leaders.

It has installed Peter Boehringer, an outspoken critic of eurozone rescues and the European Central Bank, as chair of the influential budget committee.

Through Boehringer, the AfD will be able to appoint like-minded civil servants to vacant secretarial positions and slow down the parliamentary process for policies of which it disapproves, but not gain any more voting power.

The budget committee has been chaired for the last three years by Gesine Lötzsch of leftwing Die Linke – not long ago a controversial party in its own right for its ties to the ruling party of communist East Germany, and for some, an indicator of the chairmanship’s limited political influence.

The AfD has also secured the chairmanship of two further parliamentary committees, for legal affairs and tourism.

Members of Germany’s established parties last June changed a rule allowing the oldest member of the Bundestag to kick off each new session with a speech, instead allowing the longest-serving MP to speak. This averted the privilege falling to controversial AfD politician Wilhelm von Gottberg, who has described the Holocaust as “a myth”.

During the four months in which Merkel has struggled to find coalition partners for a new government, the country’s upstart populists have slowly adjusted to working routines inside the Bundestag, filing a large number of parliamentary queries on issues centred around migration and leftwing extremism.

“The AfD tolerates Nazi slogans, gets caught up in internal fights and uses parliament as an agitprop stage,” leftwing daily taz commented in a recent op-ed. “But that doesn’t seem to affect their popularity. Apparently AfD voters want precisely that: a rightwing protest party.”