She also visited the NSW Director of Public Prosecutions Nicholas Cowdery and shadowed Margaret Cunneen SC, a Senior Crown Prosecutor and model for the character Janet King.

Janet is characterised as a "tough and tenacious" Senior Crown Prosecutor who has worked in the DPP office for ten years.

In 2014, Dusseldorp won the AACTA Award for Best Lead Actress in a Television Drama for her portrayal of Janet.

[2] Bonney explained that Janet developed from their "combined experiences", as she is a barrister and Allen is a criminal lawyer and writer.

[5] "Watching her take on this vitally important role in society, and do a job that is so emotionally wrenching, helped me build a character that I hoped did crown prosecutors justice.

"[6] In preparation for the role Dusseldorp researched numerous legal cases and observed prosecutors behaviour before judges in district courts.

She and fellow cast member Lewis Fitz-Gerald (who plays David Sinclair) visited and was welcomed by the Director of Public Prosecutions Nicholas Cowdery.

[7][8][9] Her time with Margaret Cunneen SC found her attending conferences with defence lawyers, psychiatrists and a victim.

Despite Janet's strong willed nature, she said of her portrayal, "I've tried to confess to the audience when I can that she's actually as fragile and full of feeling and love for humanity.

[7] She told Sacha Molitorisz from The Age "not to give anything away, she's in a lesbian relationship and things spin out of control a bit.

[14] Prior to Crownies final airing, ABC1 Channel Controller Brendan Dahill revealed that he wanted a spin-off to be created.

[15] On 20 August 2012, ABC TV confirmed that it had commissioned an "8-part legal and political thriller" titled Janet King.

She added "the series looks at the dilemmas of a contemporary woman who returns to work after a year's maternity leave and is flung into a shocking prosecution that involves layers of intrigue played out at the highest levels of power.

"[16] Screentime's Des Monaghan said that it had become obvious to his company and the ABC that the audience had developed "a great deal" of affection for the character of Janet and was happy to build on that success.

She stated "Janet returns to the DPP to confront a high-profile murder and a conspiracy which will threaten to unravel her life and everything she loves."

But she deliberately played her differently in Janet King and despite admiring her superior trait; Dusseldorp felt the need to tone it down.

When a secret file is leaked to the press, Janet reprimands Lina, Erin O'Shaughnessy (Ella Scott Lynch), Ben McMahon (Todd Lasance), Richard Stirling (Hamish Michael) and Tatum Novak (Indiana Evans).

Janet and Lina become conflicted over the mental state of a child accused of murder, Max Gardiner (Nicholas Bakopoulos-Cooke).

[10] Guy Davis from The Newcastle Herald branded Janet a mentor and role model to the junior solicitors.

[21][22] The Sydney Morning Herald's Ruth Ritchie said "perennial hard workers Jeanette Cronin, Marta Dusseldorp, Lewis Fitz-Gerald and Peter Kowitz are all at their best.

[25] While fellow reporter Elissa Blake described her "fearless lawyer with cool intelligence and subtle sex appeal.

"[5] While Greg Hassall believed Janet was one of the show's strong characters and Dusseldorp deserved a Logie Award.

[26] The Age's Larissa Dubecki said that Dusseldorp's portrayal of Janet taking on the case of Ben's grandfather death "exudes gravitas"; despite having to recite "clunky expository dialogue about the jury system".

[27] For her portrayal of Janet, Dusseldorp won the Best Lead Actress in a Television Drama accolade at the 4th AACTA Awards in 2014.