National lister Maureen Pugh is first in line to return to parliament following the resignation of party leader Bill English.
The former Westland District mayor lost her seat in parliament after last year's election, having appeared too far down the list and failing to secure a victory over Labour's Damien O'Connor in the West Coast Tasman electorate.
She was sworn in to parliament in 2016 after replacing former trade minister Tim Groser when he was appointed ambassador to Washington.
Mr English's resignation from parliament on Tuesday means Ms Pugh is set to make her return to the house next month.
She described Mr English's announcement as "bittersweet", in a tweet.
"He has made an enormous contribution to NZ over many years," she said.
Ms Pugh made headlines in 2016 after some of her comments were seen to be opposing the use of pharmaceutical drugs or vaccinations.
She later clarified that she supported the use of modern medicines and that her children were fully vaccinated.