Simon Bridges' chief of staff was Jamie Gray, a former public servant who became an adviser in the former Energy Minister's office.
When former Prime Minister Sir Bill English entered opposition he appointed his former senior press secretary Craig Howie as his chief of staff.
Muller would be expected to fill his office with a mixture of existing National Party staff and his own appointments.
Up to 10 are expected to resign or lose their jobs as a result of the change in leadership.
Gray and chief press secretary Rachel Morton, a former television journalist, are believed to be leaving.
Campbell was in Wellington this week meeting the new National Party leadership, several people said. She previously worked for the National Party, including as its head of research between 2000 and 2003, according to her LinkedIn profile.
Over the weekend Campbell updated her LinkedIn profile to mention charitable positions she holds. She also serves as a director of Sport Waikato.
In 2019 she was named as the Institute of Directors Waikato branch emerging director of the year.
During her time in lobbying, Campbell is said to have played a behind the scenes role in helping secure support for legislation which allowed gay marriage.
Former Green Party MP Kevin Hague described Campbell as "very smart, stategic and valued-driven".
Muller declined to comment on the appointments to the Herald, saying he expected to be announcing changes under his leadership on Monday.
Lobbyist and political commentator, Matthew Hooton, also a former National Party staffer is also said to be lined up for a role, with suggestions on Sunday that it would be strategic communications advice.
So far Muller's only announcement has been that he will be taking on the small business portfolio and intends to continue in that role as Minister for Small Business should he become Prime Minister.