The Department of Parliamentary Services' sacked boss, Carol Mills, says she is leaving Parliament in a better shape than she found it.

Ms Mills, who oversaw much of the running of Canberra's Parliament House before she lost her job, told her colleagues on Friday that the benefit of changes she made would become apparent in the months and years ahead.

She had been under pressure on a number of fronts for months and was sacked on Tuesday by her bosses, House of Representatives Speaker Bronwyn Bishop and Senate President Stephen Parry.

But in an upbeat message to staff on Friday, Ms Mills said the department's public servants should be proud of the work they had done under her leadership.

"Reform is never easy, and reform pursued on multiple fronts simultaneously is very challenging," the former secretary wrote.

"The new systems and policies we have put in place to bring greater rigour, effectiveness and transparency to our work have already made a difference, but I know that their real effect will become more apparent in the months and years ahead.

"You can be proud of the reforms you have helped to bring about, in every area of DPS activity."

Senator Parry and Ms Bishop announced the dismissal in a tersely worded message on Friday morning.

"Today we announce that Ms Carol Mills is no longer the secretary of the Department of Parliamentary Services, effective from 21 April 2015," the statement read.

"The Parliamentary Librarian, Dr Dianne Heriot, will continue to act as secretary until further notice."

Senator Parry's office said on Friday morning he would make no further public comments.

Ms Mills, a former high-ranking NSW bureaucrat, had been criticised severely by the Senate's privileges committee over claims her department used the building's CCTV network to spy on one of its public servants who was leaking material to Labor senator John Faulkner.

Ms Mills lashed out at the committee in February, arguing she had been denied procedural fairness and natural justice and that the senators relied on dodgy advice from the secretary's in-house rival, clerk of the Senate Rosemary Laing.

Labor senators intensified their pursuit of Ms Mills and were joined by independents, Greens and Liberals last month, alleging she failed to declare that a photographer hired for tens of thousands of dollars to photograph the Parliament was a neighbour of hers in Sydney.

The timing of the committee hearing could hardly have been worse, coming on the heels of an Australian National Audit Office report that found problems with some contracts handled by her department.

The artist, Anne Zahalka, was paid $40,000 dollars to photograph Parliament's workers going about their daily business as part of the building's 25-year celebrations in 2014.

Liberal senator Cory Bernardi declared during a hearing that the contract "stinks to high heaven".

The feud between Ms Mills and Dr Laing exploded publicly in August 2014 when the clerk tried to derail the secretary's chances of landing the plum job of clerk of Britain's House of Commons.

Dr Laing wrote to retiring Commons clerk Sir Roger Roberts, whom Ms Mills had been frontrunner to replace, with a stinging attack on Ms Mills and her professional abilities.

The letter promptly went public as part of a concerted campaign by conservative forces to derail Ms Mills as Commons speaker John Bercow's choice for the clerk's job after she had been headhunted for the role.