Ms Lawder was announced as the replacement for former Canberra Liberals MLA Zed Seselja on Monday, following a countback of ballot papers in the southern electorate of Brindabella.

Her first words after learning she had claimed the seat by just eight votes ahead of Tharwa identity Val Jeffery were ''how's Val?''

''I think that's a real measure of the woman that her first concern was for somebody else and not herself,'' Opposition Leader Jeremy Hanson said.

''I think that's the nature of Nicole Lawder and that's why she'll be so great to have on our team.''

Under the ACT's Hare-Clarke electoral system, byelections are not held to fill vacancies.

Seven candidates contested the seat, with Ms Lawder declared the new Liberal member for the Assembly by acting ACT Electoral Commissioner Andrew Moyes. Ms Lawder, the chief executive for Homelessness Australia, was at a national conference in Melbourne for DisabilityCare Australia at the time of the announcement.

Her husband, Peter Badowski, called her with the news.

''It was a little bit unexpected. I thought Val would have a good chance and of course it was extremely close,'' Ms Lawder said.

''I am excited. Over the next few days I'll talk to Jeremy and work out what the next steps are.'' Ms Lawder said she ''firmly believed in being part of an effective team''.

''Before I get too carried away with what I personally hope to achieve it will be about working with my Assembly colleagues on what is the best way to progress our issues,'' she said.

But her personal passions lie in the disability and community sectors, where she began working after her brother was shot at Monash University in 2002.

''That was a traumatic time for our family,'' Ms Lawder said.

''At that point, while I was in the hospital waiting room, I thought if I died what would people say about me? What have I achieved?

''At that point I decided I wanted to do something that would bring about holistic change in the community.''

Ms Lawder will be sworn in at the next Assembly sitting in August.