Mr Smith - who became Scotland’s youngest MEP when he was elected in the 2004 European Parliament election at the age of 30 - told politicians in Brussels at an emergency meeting to discuss Brexit, that he was ‘proudly Scottish and proudly European’.
Mr Smith added: “I want my country to be internationalist, cooperative, ecological, fair, European.
“And the people of Scotland, along with the people of Northern Ireland, and the people of London and lots and lots of people in Wales and England also, voted to remain within our family of nations. “I demand that that status and that esprit européen be respected.
“Colleagues, there is a lot of things to be negotiated. We will need cool heads and warm hearts.
“But please, remember this: Scotland did not let you down. Please, I beg you, chers collègues, do not let Scotland down now.”
Mr Smith received a standing ovation from his colleagues in the Greens/European Free Alliance group, following his speech.
His remarks followed a speech by Nigel Farage, who told fellow MEPs “you’re not laughing now” as he was barracked and booed at the meeting.
The Ukip leader accused them of being “in denial” about the euro crisis, immigration and the imposition “by stealth, by deception, without ever telling the truth” of a political union.
Offering a tongue in cheek “thank you for the warm welcome”, he told them: “When I came here 17 years ago and said I wanted to lead a campaign to get Britain to leave the European Union you all laughed at me.
“Well I have to say you’re not laughing now are you?”
As the session was disrupted by constant shouts of dissent, Parliament president Martin Schulz was forced to intervene, warning members that “one major quality of democracy is that you listen to those even if you don’t share their opinion”.