Attorney General John Morris QC will have to give evidence in person in the sexual discrimination case being brought by barrister Josephine Hayes.
Croydon Employment Tribunal last week ruled that Morris will have to appear at the full hearing on 21 June next year.
Hayes brought the discrimination claim over the appointment by Morris, using the traditional secret soundings procedure, of Philip Sales as First Treasury Counsel or "Treasury Devil".
Hayes is arguing that Sales' appointment was the subject of an "old boy network".
Last month Morris announced that he would be advertising for 50 new government civil counsel posts for the junior bar, in what he claimed was a new era of "opportunity and transparency" for government appointments.
Morris is the second senior figure at the Lord Chancellor's Department to be called on to give evidence at a discrimination case.
Croydon Employment Tribunal ruled that the Lord Chancellor, Lord Irvine of Lairg, would have to appear in person at the racial and sexual discrimination case brought by Jane Coker and Martha Osamor.
Coker and Osamor brought the case over Lord Irvine's controversial appointment of former Herbert Smith partner Garry Hart as his special adviser.