The Turnbull government has officially backed a Tasmanian mayor to replace Jacqui Lambie in the Senate, potentially frustrating Pauline Hanson's plan to seize a fourth seat for One Nation.

In a submission to the High Court released on Monday, government solicitor Stephen Donaghue argues there is no constitutional barrier to prevent Devonport mayor Steve Martin taking up the seat.

Devonport mayor Steve Martin could soon become a senator. Credit:Cordell Richardson

Mr Martin was second on Ms Lambie's ticket at the 2016 election. Ms Lambie quit last month after getting caught up in the dual citizenship fiasco that claimed careers across Federal Parliament.

But question were instantly raised about Mr Martin's own eligibility, with claims his role as a councillor and mayor could be considered "an office of profit under the crown" – also forbidden under section 44 of the constitution.