One Labour peer said it would be “obscene” if Britons working for EU organisations were barred from taking part.
The Conservatives promised in their manifesto to introduce “votes for life”, but Cabinet Office minister Lord Bridges of Headley said he could not give a commitment that the change would be made in time for the referendum, which is due to take place by 2017.
British citizens living abroad are at present not allowed to vote in parliamentary elections after they have been out of the country for 15 years.
At question time in the House of Lords, Tory peer Lord Lexden said there were an estimated two million Britons living in other EU countries, and the issue led to “very strong feelings”.
Labour peer Lord Tomlinson said there was “something very wrong” if British people who had devoted their careers to working in the European Union were unable to vote.
“It is particularly obscene that they should be denied a vote when it comes to a referendum on their future membership of the European Union,” he said.
Liberal Democrat Lord Wallace of Saltaire called for some accurate information on the number of people involved and where they lived.
Lord Bridges told peers: “The Government is committed to making a permanent change to remove the 15-year time limit on the parliamentary voting rights of British citizens living overseas.
“The Government is currently considering the timetable for doing so, and will set out more detail in due course.”
Lord Bridges said there were 5.2 million British-born migrants living overseas.
He said more than 105,000 British citizens living abroad were registered to vote in this year’s general election, which was more than three times the previous highest number.