EU judges have dismissed a case brought by the group, which included a Second World War veteran.
Harry Shindler, a 97-year-old living in Italy, was among the 13 expats who complained that Brexit would deprive them of EU citizenship.
But on Monday, the EU’s General Court dismissed the action as inadmissible. It said the EU Council's decision to accept notification of Britain’s withdrawal did not in itself carry any definite consequences for their rights.
Expats didn’t vote, will lose their European citizenship, lose a lot of rights before March 2019 and couldn’t challenge this loss for first Europeans judges. Unacceptable for our European citizenship. The fight goes on with an emergency appeal before European Court oj justice— FOUCHET (@julienfouchet1) November 26, 2018
Julien Fouchet, a French lawyer acting for the group, said he would appeal to the Court of Justice, the EU's top court.
"Unacceptable," he tweeted. "The fight goes on."
Mr Shindler had demanded that all expats be given a vote in the referendum to London's High Court. Judges there ruled two months before the 2016 referendum that this would be too difficult for the authorities.
On Tuesday, the European Court of Justice, in Luxembourg, will hear a case brought by Scottish politicians who oppose Brexit and want judges to rule on whether the Article 50 notification process can be unilaterally revoked by the British government.
They hope that can strengthen a campaign to have Brexit halted altogether, although Prime Minister Theresa May continues to insist Brexit will go ahead.
Additional reporting by Reuters.