Sinn Féin MEP Martina Anderson wore James McClean's Ireland jersey from the 2-0 win against Gibraltar in June during a European Parliament session on Wednesday morning.
The Derry native did so during a debate on Brexit.
Speaking to GUE/NGL in a video broadcast on Instagram, Anderson explained why she wore the jersey.
"I was proud to wear it today," she said.
I felt it sent a signal to the people of Gibraltar who like ourselves in the North of Ireland voted overwhelmingly to remain in the EU.
They are going to have difficulties crossing the border into Spain as a consequence of a no-deal Brexit.
I put this shirt on, it was international solidarity with Gibraltar.
Holding her Irish passport during the debate, Anderson said it entitled her to remain an EU citizen.
"A chairde, my Irish passport says that it is the entitlement and birthright of everyone born on the island of Ireland to be part of the Irish nation," said Anderson, who has been an MEP since 2012.
"As this resolution clearly states we Irish in the North of Ireland are therefore entitled to EU citizenship where we reside.
"Whilst the backstop is essential to prevent a hardening of the border partitioning Ireland, to protect the all-Ireland economy and North-South cooperation, it takes us out of the EU against our will - we in the North of Ireland voted to remain.
"It is important this parliament recognises as stated in the resolution the legitimacy of whatever choice is freely exercised by the majority of the people in the North of Ireland to our right to change its status, to our right to self-determination.
"As recognised in the Good Friday Agreement in British and Irish law, the European Council statement stated that in the event of Irish reunification all 32 counties would remain in the EU.
"The French president Macron stated that the solution to the Brexit problem is Irish reunification. Lord Ashcroft's opinion poll shows a majority in favour of Irish reunification.
"The Good Friday Agreement provides a peaceful, democratic pathway back into the EU for the people of the North of Ireland and that should be respected by all."
