Rosa McLaughlin, who took up her post at St Mary's College in Londonderry last month, was convicted in 1998 of IRA membership and collecting information useful to terrorists.
The school and the Council For Catholic Maintained Schools (CCMS) last night defended the appointment of 40-year-old Miss McLaughlin saying that all relevant procedures had been followed.
However, parents have expressed anger that they were not told by the school about the new teacher's criminal past.
Miss McLaughlin was a 26-year-old school teacher in east Belfast when she was found guilty of spying on Bangor RUC station and collecting information on former RUC Assistant Chief Constable Trevor Forbes.
She had been recruited by the IRA in her fifth year of studies at Queen's University in Belfast.
Miss McLaughlin was sentenced to three years in jail but was freed upon conviction after spending 18 months on remand.
The sentencing judge at the time warned her that her career as a teacher had been destroyed and that he was satisfied she would "never be employed in the United Kingdom as a teacher".
However, Miss McLaughlin went on to excel in her career within the education sector.
She became a senior teacher in Northern Ireland's only post primary Irish Medium school, Colaiste Feirste, Belfast, before becoming Inter Schools liaison manager for the Foyle Learning Community.
Miss McLaughlin was appointed vice principal of St Mary's College in January and is just in the first few weeks of her new post.
When contacted by the Belfast Telegraph about her previous convictions Miss McLaughlin said: "You have taken me completely by surprise.
"I want to speak to my principal and the governors."
St Mary's College last night defended Miss McLaughlin's appointment saying that she was the most qualified for the role of vice-principal.
A spokeswoman for the school added: "As with all our employment procedures, everything was carried out in accordance with both the law and relevant statutory agencies."
St Mary's school principal Marie Lindsay also said: "Whilst I am aware of the background to this particular matter, I do not consider it appropriate to comment further on personal information relating to individual members of staff."
A CCMS spokeswoman said: "The council in ratifying this appointment was satisfied that the Board of Governors followed all the relevant procedures."
The school and the CCMS were asked by the Belfast Telegraph if any moves had been taken to advise parents of Miss McLaughlin's conviction.
However, neither commented on this.
The Department of Education also declined to comment on whether it believed it was appropriate for someone with a terrorist conviction to be allowed to teach.
A spokesman for the department commented: "Teachers are appointed to posts by the body responsible for the management of the school in which the vacancy has arisen.
"The Department of Education does not appoint teachers."