The Both Lives Matter group, a movement that includes the Evangelical Alliance in Northern Ireland, found the figure by comparing the rates of abortion in Scotland - which has the lowest abortion rates in the UK and is culturally most similar to Northern Ireland.
The report then estimates the number of abortions carried out for Northern Irish women in England and Wales based on UK Department of Health data which is cited in academic literature by pro-choice advocates.
The difference between these figures is the number of people alive today because the 1967 Act was not enacted in Northern Ireland.
Economist Dr Esmond Birnie said: "There is obviously no absolute certainty about what 'an alternative Northern Ireland' would have looked like if the 1967 abortion legislation had been applied here as in GB.
"However, what Both Lives Matter have done, as the basis for their report, is to make plausible and cautious estimates as to what might have happened.
"The estimates suggest that 100,000 people - men, women and children - are alive in Northern Ireland today."
Dawn McAvoy of Both Lives Matter said: "The debate around abortion is in danger of becoming polarised by those only concerned with the unborn child on the one hand and those solely concerned with the rights of the women on the other. The reality is that both lives matter.
"The contrast with England and Wales is stark. There one in three women by the age of 45 will have had an abortion and for every four children born alive, one has been aborted.
"The act allows abortion up to birth for disability and when Downs' Syndrome is diagnosed in utero, nine out of 10 babies are aborted. This isn't the best care for women and children."
