Lady Sylvia Hermon last night said she feared Brexit could result in a border poll that would lead to a united Ireland.
Speaking on BBC NI's The View programme, the North Down independent unionist MP said: "I am worried about the long term consequences of Brexit.
"In my lifetime I never thought I would see a border poll. I am now convinced that I probably will see a border poll."
Lady Hermon has been a consistent opponent of Brexit, and voted against the legislation which triggered Article 50, beginning the UK's EU exit.
Last week, she said she was worried that Brexit would mean a return to violence in Northern Ireland.
The most recent border poll in Northern Ireland was held in 1973.
Meanwhile, Brexit Secretary David Davis has reiterated his commitment to avoiding a hard border in Ireland after Brexit, amid a row over customs arrangements.
He told MPs at Brexit questions: "We have said categorically that there will be no physical infrastructure or related checks and controls at the border between Northern Ireland and the Republic of Ireland. We've set out our clear commitments on borders and put forward two potential customs models, which were just referred to earlier.
"The best solution to solve the Northern Ireland/Ireland border is through the deep and special partnership between the United Kingdom and the European Union, recognising the unique circumstances of Northern Ireland."