Henry Reilly was UKIP's Northern Ireland candidate in last year's European elections, receiving more than 24,000 votes.
The Newry, Mourne and Down councillor was suspended from the party in September, although Mr Reilly denied at the time that this had happened.
A UKIP spokesman confirmed on Tuesday that Mr Reilly had been expelled.
"At midday, Henry Reilly was advised that resulting from his suspension, a disciplinary meeting held yesterday took the decision to expel him from UKIP membership," he said.
"There will be no further comment on this internal party decision."
In September, UKIP's leader in Northern Ireland, David McNarry, confirmed to the BBC that Mr Reilly had been suspended after party leader Nigel Farage visited Belfast.
However, Mr Reilly, who is from Kilkeel, County Down, had described it as a "technical issue" involving a discussion with a journalist and denied being suspended.
One of UKIP's most high profile figures in Northern Ireland has been expelled from the party.