The bill would also ensure that they would have to wait at least five years before they could apply to return to the classroom, said Education Minister Liz Sandals.
The automatic penalty wouldn't apply to teachers convicted of other criminal offences, but they can still lose their licence to teach, she said.
"The criminal convictions that parents are absolutely concerned about are the ones that have a negative impact and bring harm to a student," she said.
"And what we have highlighted are those which are the most egregious of the sexual offences, where there would be mandatory revocation."
Currently, it's up to the Ontario College of Teachers — the provincial regulatory body — to decide the penalty, such as suspend their teaching certificates. It also decides how long a teacher would have to wait before they can seek reinstatement.
But in the "vast majority" of cases, a teacher convicted of a serious offence doesn't get their licence back, Sandals said.
"They have the ability to reapply," she said. "The fact that you re-apply doesn't mean that will be granted."
And even if they got their licence back, that doesn't mean they'll be hired, she added.
Teachers who are convicted of serious offences often have their licences permanently revoked, said college registrar Michael Salvatori.
In many cases, the panel that considers their application to return to the classroom upholds the previous decision to revoke the licence, he said.
"It would be rare for what we consider the very most serious proven allegations of sexual abuse for a member to be able to reinstate, because it goes back to a discipline panel, similar to one that would have made that revocation in the first place," he said.
Teachers can appeal the decision, but they can't keep re-applying, he said.
Under the proposed rules, school boards would have to alert the College when they've disciplined or fired a teacher for misconduct. The College would also be allowed to share information with a school board if the subject of a complaint poses an "immediate risk" to a student, she said.
"This just clarifies the circumstances in which the school boards must report to the College the discipline that they have imposed on a teacher," the minister said.
There would be new timelines to resolve cases more quickly, she said. When hearing cases relating to the conduct of a principal or vice-principal, the disciplinary panel must include a principal or vice-principal.
The draft changes come two years after the College commissioned a review of its investigation and disciplinary procedures. It said it approved most of the 49 recommendations last year and directed the government to make the necessary legislative changes.
Sandals noted that the College has already implemented some of the recommendations, such as posting decisions of disciplinary proceedings on its website.
According to its annual report, the College received 230 complaints in 2011, 38 of which went to the discipline committee.