The former Liberal chief minister said she has red tape in her sights and wants to lower the cost of doing business in Australia.

Ms Carnell said she loved Canberra and was looking forward to returning to the capital.

''It is an opportunity to get back to Canberra and an opportunity to do something really important,'' she said.

The former small business owner and chemist became the ACT's third chief minister in 1995, soon before the Coalition came to power in a federal election.

Ms Carnell said she had learnt lessons on how to make the ACT a business-friendly place that she would take into her new role.

She served as chief minister until 2000, when she resigned before an expected no-confidence motion over her handling of redevelopments at the now GIO Stadium in Bruce.

Ms Carnell went on to head the Australian Food and Grocery Council and two years ago took over as chief executive of beyondblue, but she said her appointment at the not-for-profit mental health organisation was only ever meant to last two or three years.

She said she was a board member who stepped into the role after a couple of CEOs did not work out and cites the introduction of a popular online chat service for people wanting to speak to a mental health professional as one of her achievements in the job.

Although she remains a member of the Liberal Party, Ms Carnell said she would never again return to politics.

Beyondblue chairman Jeff Kennett said Ms Carnell would remain CEO of the organisation until May and, in the interim, a search would begin for her replacement.

''Kate leaves beyondblue in a much stronger position than when she was appointed CEO, and she has helped develop a solid strategic direction for the organisation,'' he said.

Chamber executive chairman Peter Hood said Ms Carnell's small business background, political leadership experience and industry association skills would benefit the organisation's role as the voice of Australian business.