Gemma White QC said there was a "significant problem" about the way some MPs treated those who worked for them.
She said the House of Commons authorities had been too slow to act in response to previous reports into the issue.
"Some staff of Members of Parliament are subject to an unacceptable risk of bullying and harassment, including sexual harassment, at work," she said.
"Most Members of Parliament treat their staff with dignity and respect but the problem of bullying and harassment is sufficiently widespread to require an urgent collective response.
"Recent steps taken by the House of Commons to address bullying and harassment across the Parliamentary community do not engage sufficiently with the particular issues faced by members' staff, who are in a uniquely vulnerable position because they are directly employed by Members of Parliament.
"Many describe the idea of complaining about bullying and harassment under the new complaints procedure as 'career suicide'.
"They also often have strong party and personal loyalties which constitute significant barriers to complaint."
In response to the report, the House of Commons Commission - which is responsible for the administration of the Commons - said: "We condemn bullying and harassment of MPs' staff and offer our full support to anyone in the parliamentary community who has suffered in this way.
"The commission does not employ the staff of MPs as they are employed by MPs themselves, or via political parties.
"However, the commission takes very seriously its responsibility to ensure that Parliament is a modern workplace."
Ms White's investigation was ordered last year by the then leader of the House, Andrea Leadsom, following a highly critical report by Dame Laura Cox which highlighted the widespread bullying and harassment of staff.
In her findings, Ms White said such behaviour had been "tolerated and accepted" for too long.
"It has seriously affected the health and welfare of far too many people," she said.
"There is a pressing need for a collective response to what is clearly a significant problem.
"I am concerned by the amount of time it has taken to act on recommendations from previous reports and would urge the House to move more swiftly.
"While the House of Commons is not alone in tolerating these behaviours, it is the home of our policy makers and a taxpayer-funded institution. It should therefore be at the forefront of good employment practice."