But the 63-year-old says that following last month's historic meeting between opposing leaders Gerry Adams and Ian Paisley and the tentative agreement over power-sharing at Stormont, he is now able to make the move.
Speaking to the Today programme, Lord Trimble said: "Now that Northern Ireland's settled, I'm now free to follow what has been an ambition for many years.
"In groups of this nature there's always a culture to each particular organisation. I know something about the Conservative party, I've attended many of its meetings, both at constituency level as well as at conference level over the years."
In relation to any role he could fill at his new party, Lord Trimble said that he had spoken to Tory leader David Cameron and told him he "didn't want to rush things".
"I think the first thing I should do is get accustomed to their own way of doing things."
Lord Trimble was awarded a Nobel peace prize for his part in the Good Friday Agreement in 1998, but he stepped down as leader of the Ulster Unionists when he lost his parliamentary seat.
Mr Cameron has previously spoken of his admiration for David Trimble, saying that he "got to know him a little bit" during the last parliament.
Lord Trimble added that he was exploring a "wider horizon" and that he hoped the people of Northern Ireland would do the same.
"There is a larger context and I hope that politics in Northern Ireland doesn't become too introverted in the way that it has been too often in the past," he said.
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