Alyn Smith told his fellow parliamentarians in Strasbourg that the UK’s expected departure from the European Union was a “self-inflicted disaster”.
He continued: “If Scotland is removed from our family of nations against our will, against our clearly democratically-expressed view, if we are removed against our will, independence will be our only route back.
“Cher colleagues, I’m not asking you to solve our domestic discussions. I am asking you to leave a light on so we can find our way home.”
The speech received warm applause from the room, including from Donald Tusk, the president of the European Council.
But it was greeted with mockery by at least one former UKIP MEP.
Almost two thirds of Scots voted to remain in the European Union in the 2016 referendum, with Nicola Sturgeon and others complaining that the Brexit vote means the country now faces having to leave the trading bloc against the wishes of its people.
The First Minister is due to set out her thinking on a second Scottish independence referendum in the near future, but said recently that another vote on the issue was “as inevitable as it’s possible to be”.
Mr Smith added: “Every single party in Scotland except the Conservatives are united around the view that the best Brexit is no Brexit.
“So colleagues, please, don’t close the door on us now. There are a lot of us in Scotland and across the UK, working hard to turn this round, to serve our citizens, to remain within this family of nations.
“In what might be my last speech in this place after 15 years serving our European people, we don’t know what’s in the UK’s future. We don’t know what’s in any of our future and the forces of populism are gathering in all our nations.
“We don’t know what’s in the UK’s future but I do know Scotland is a European nation.
“We celebrate international solidarity. We celebrate freedom of movement.
“If the European Union didn’t exist, we would have to invent something like it, and Scotland would want to be part of it.”