Ms Stoker was approved by Queensland parliament on Wednesday after winning the LNP pre-selection to replace the former attorney-general.

The 35-year-old barrister's swearing-in was delayed on Thursday morning, with the governor-general waiting on the correspondence he needed to tick off the appointment.

The ceremony took place at the beginning of Question Time.

Ms Stoker has already come under fire from Queensland Labor, who criticised her for speaking at a pro-life rally in Brisbane at the weekend.

"Abortion is a highly controversial issue, even in my own party which is libertarian," crossbench senator David Leyonhjelm told reporters in Canberra on Thursday.

"(The Liberals) are a broad church, so you could expect there would be quite a range of opinion there."

Mr Brandis was officially appointed Australia's High Commissioner to the UK earlier in the week after announcing last year he would leave politics.

Ms Stoker's entry to the upper house brings the Senate to its full complement of 76, ending a 250-day stretch - the longest since Federation - with at least one vacancy.

But that might be short-lived, with a constitutional cloud hanging over Labor's Katy Gallagher as to when she renounced her British citizenship.

Australian Associated Press