Four right-wing parties in the Netherlands said on Wednesday that they had reached a preliminary agreement to form a government that would exclude Geert Wilders, a populist politician, from becoming prime minister.

The breakthrough came hours before a midnight deadline and was the result of nearly six months of negotiations. After the negotiators expressed optimism about the chances of forming a government, the members of the parties that will make up the coalition said they would support the preliminary agreement.

“This won’t go wrong,” Caroline van der Plas, the leader of the Farmer Citizen Movement, a populist pro-farmer party, told reporters on Wednesday. In response, Mr. Wilders posted two prayer hands and a sun emoji on the social media platform X.

The agreement would still largely depend on Mr. Wilders’s party, Party for Freedom, which won elections decisively last fall, sending shock waves through the Dutch political system.