Manuel Pangilinan quit after admitting he had borrowed from US President Barack Obama, TV host Oprah Winfrey and children's author JK Rowling.
He stepped down after it was revealed on the Facebook website that his address to students was not original.
Mr Pangilinan had in the past spoken up for ethics and morality.
He said he decided to step down as chairman of the board of trustees of Ateneo de Manila University in the capital, Manila, to spare the university any criticism.
In a statement published on the university website, Mr Pangilinan said he was embarrassed by the speech he made at the university last month.
He said he had had some help in drafting his remarks, but took full responsibility for them.
"I have been told last night that portions of my graduation remarks - in particular my address to the Schools of Humanities and Social Sciences - had been borrowed from certain other graduation speeches.
"I had taken a look at the side-by-side comparison on Facebook, and must admit to this mistake."
Mr Pangilinan is also head of the Philippine Long Distance Telephone Company.
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/1/hi/world/asia-pacific/8602674.stm
