Three female students in black 'Repeal' sweaters sat directly behind the Taoiseach during his visit to Queen's University.
The women's position in the audience in the Great Hall meant that it was difficult to photograph Leo Varadkar without getting their message across too.
The Irish government is to hold a referendum on repealing the Eighth Amendment, which has been a long-term goal of pro-choice campaigners. The amendment gives the foetus an equal right to life as the woman.
Lucy Gault, Rachel Powell and Jessica Elder said they were delighted to have been able to send out a "clear, strong message" on abortion and uphold the record of students as "proud advocates for social justice".
Ms Powell told the taoiseach that plans to hold the referendum in May or June would disenfranchise many students who leave Ireland during the summer.
Mr Varadkar said a date hadn't been set yet, but the Republic had previously held June referendums.