And while Ingham will stand by the PRCA's decision, saying it was part of the body's "responsibility for upholding standards", he will say that he feels "incredibly sad" for those people who no longer have jobs.
Earlier this month, Bell Pottinger became only the second agency in the last 10 years to be excluded from the PRCA, following a guilty ruling on a complaint about its now infamous work in South Africa.
On the ruling, Ingham will say: "A couple of people have said I enjoyed the expulsion of Bell Pottinger. Nothing could be further from the truth. It was the most stressful period of my professional life. The toughest decision the PRCA has ever made.
"Let me be clear. The responsibility for the destruction of Bell Pottinger lay with Bell Pottinger - and with Bell Pottinger alone. But the responsibility for upholding standards lay with us. And I make no apology for us carrying out that responsibility."
Ingham will add that in the "rare" instances when malpractice does occur in the PR industry, the PRCA will take appropriate action.
"As Richard Edelman put it - this was a proud moment for PR. The moment we proved that we have standards. And that those standards are enforced."
The conference, titled Communicating in Turbulent Times, is taking place at BAFTA in London and includes discussion from experts from across the PR industry.
To coincide with the event, the PRCA has revealed that its revenue has grown from £2.89m during the 2015/16 financial year to £3.16m during 2016/17, with its membership bolstered by 31 in-house teams and 43 agencies joining in the period.
During his opening address, Ingham will say: "Ten years ago, the PRCA was essentially an afterthought. Today, it is our industry's undisputed professional body. PRCA membership is the gold standard of ethical professionalism. The only rock solid guarantee clients and colleagues have that a PR practitioner is an accountable one."