Former MLA James Milligan will return to ACT politics as the new member for the seat of Yerrabi.

Mr Milligan takes over a vacancy left by from former Opposition Leader, Alistair Coe who formally resigned from the Assembly earlier this month.

The Canberra Liberals member was first elected to the Assembly in the seat of Yerrabi back in 2016 but was defeated at the last Territory election with Leanne Castley picking up the second liberal held seat.

Mr Milligan will be formally sworn in when the Assembly next sits on Tuesday 30 March.