NSW Labor senator Kristina Keneally may need to take a short break from Bill Shorten's election campaign to testify in the defamation case brought against David Leyonhjelm by SA Greens senator Sarah Hanson-Young.

Key points: Ms Hanson-Young said her character had been attacked by David Leyonhjelm

Ms Hanson-Young said her character had been attacked by David Leyonhjelm The court heard both parties were warned the trial was likely to coincide with the election

The court heard both parties were warned the trial was likely to coincide with the election Senator Keneally is among 10 witnesses expected to provide evidence to the trial

The Federal Court in Adelaide has heard the trial will begin on April 29, at the height of the federal election campaign.

Senator Hanson-Young is suing Mr Leyonhjelm for defamation, claiming her character had been attacked through statements that she was a misandrist and a hypocrite in television and radio interviews last year.

The former Liberal Democrat senator, who recently failed in his election bid for the NSW Upper House, has denied he defamed the Greens politician.

Today, the Federal Court heard Senator Keneally was among 10 witnesses who were expected to provide evidence to the trial.

Senators Derryn Hinch and Stirling Griff are expected to be called to give evidence, while Senator Hanson-Young and Mr Leyonhjelm will also testify.

The trial is due to start on April 29, at the height of the federal election campaign. ( ABC News )

Sue Chrysanthou, the lawyer for Senator Hanson-Young, said several senators would be expected to undergo a short cross-examination at court.

She requested the witnesses be allowed to appear via video link due to the "exorbitant" cost of flying them to Sydney.

However, Justice Richard White was reluctant to agree, and said the witnesses were available and had been given plenty of notice.

He told the court he had warned the parties that the timing was likely to coincide with an election.

Ms Chrystanthou and Mr Leyonhjelm's lawyer, Kurt Stoyle, both confirmed that attempts to find a resolution through mediation had failed.

'This is something I feel very strongly about'

Senator Hanson-Young is seeking re-election while Mr Leyonhjelm has conceded his "life as a politician is over" following the NSW state poll.

In a blog post published earlier this week, Mr Leyonhjelm was particularly critical of the Liberal Democrats, which he led for more than a decade.

"While this is not a personal tragedy for me [I was always a fairly reluctant politician], it is concerning for the Liberal Democratic Party," he wrote.

"I wish I could say the party is in good hands, but I fear that is not the case.

"The National Executive does not inspire confidence."

Ms Hanson-Young commented on the case while the Greens launched their environmental policies at a campaign event in Adelaide.

Senator Hanson-Young and Greens Leader Richard Di Natale launched the party's environmental policies in Adelaide today. ( AAP: Roy VanDerVegt )

"It is in the middle of the election campaign, and that's up to the court and the judge of course," Senator Hanson-Young said.

"This is something that I feel very strongly about.

"I've taken this action because no woman and no girl deserves to feel bullied in their workplace, and treated with disrespect by her colleagues."

Last November, the court dismissed an application by Mr Leyonhjelm to have the case against him thrown out.

He called on the court to stay the proceedings, arguing that the case amounted to an abuse of process because he could not mount a defence without breaching parliamentary privilege.

The trial is expected to run for five days.