The High Court will hear a challenge to the ACT's same-sex marriage laws less than a week before the first wedding ceremonies will take place.

On Monday, Chief Justice Robert French told a directions hearing the case, brought by the federal government, would be heard by the full bench of the court in a two-day hearing on December 3 and 4.

It is likely that the High Court will be considering its decision when the first same-sex marriages take place from December 8.