Joanne Hayes is officially a National list MP, replacing Katrina Shanks who resigned her seat at the end of last year.
The Electoral Commission has made the formal declaration of Mrs Hayes' election to Parliament.
Mrs Hayes unsuccessfully contested the Dunedin South seat for National in 2011.
She is now based in Manawatu and is director of community relations for tertiary institution Whanganui UCOL.
Mrs Hayes is of Ngati Porou, Ati Haunui A Paparangi, and Rangitane ki Wairarapa descent.