Frans Timmermans, the former EU climate chief and leader of the opposition GreenLeft–Labour party, said the pact was “disastrous”.
Mr Wilders, an ardent eurosceptic, was forced to ditch a campaign promise to hold a Brexit-style Nexit referendum and sacrifice his hopes of being prime minister to get the deal over the line.
The prime minister has not yet been named but the leaders of the other parties are also ruled out.
One name being mentioned is Ronald Plasterk, a former Labour minister who chaired an earlier round of coalition negotiations.
‘Truss lettuce’ stands for prime minister
However, some commentators are sceptical that the new government will last. One podcast, inspired by a British newspaper stunt over Liz Truss’s ill-fated premiership, has already set up a lettuce in competition with Mr Plasterk to see which lasts longest.
The Netherlands joins Hungary and Poland’s previous nationalist government in challenging EU migration policy.
Brussels will resist, as EU countries have already agreed on their migration pact and opt outs are usually discussed in the negotiating phase.
“We have a new pact on migration and asylum, which has been voted upon and confirmed and therefore has to be applied,” the European Commission’s chief spokesman said in Brussels.
“This legislation will be applied and the commission will play its role in making sure it is.”