Rev Smyth (94) served as MP for South Belfast from 1982 until 2005.
He took the seat in a by-election after the sitting MP, Rev Robert Bradford, was murdered by the IRA in November 1981.
Rev Smyth also served as Grand Master of the Orange Order for 26 years.
Ulster Unionist leader Mike Nesbitt led tributes, saying: “I am terribly sorry to hear of the passing of Martin Smyth.
“From my days as a broadcast journalist, he was an ever-present heavyweight in local politics, whose views were always important.
Rev Martin Smyth pictured in 1970
“He may not have been as prominent as others in the public sphere, but hugely influential behind the scenes.
“He was another of that fateful generation of what we so euphemistically call ‘The Troubles’ whose imprint will last forever.”
He will be remembered for his quiet confidence but also his power
Former UUP leader Lord Empey recalled Rev Smyth leading the way in Parliament in his pursuit of legislation to assist the disabled.
“It was a consistent theme of his representation of the people of Northern Ireland,” he said.
“While well known and respected for his defence of unionism, his compassion for those less fortunate shone through”.
Jim Nicholson, a former UUP MEP, said his late colleague was “a titan” of unionism.
“He will be remembered for his quiet confidence but also his power as an orator and champion of Ulster Unionism,” he added.
Former UUP MLA Danny Kennedy said: “He was a deeply committed Christian and an unapologetic Unionist. He gave leadership in difficult and different times.”
DUP leader Gavin Robinson also offered his condolences to Rev Smyth’s family.
Martin Smyth (second left), with Bill Craig, George Allport and Stanley Morgan at the launching of the Ulster Vanguard Association in 1972.
The East Belfast MP said: “A stalwart of unionism, he stepped forward in South Belfast at a most volatile time.
“Firm and faithful, he represented his constituents and NI with a strong sincere strength and unswerving belief in the Union.”
TUV leader Jim Allister said Rev Smyth “served Protestantism and unionism for many years through some of the worst of the terrorist campaign”.
The Grand Orange Lodge of Ireland described Rev Smyth as “a leader of unwavering principle and determination through often difficult times and a stalwart of the Orange cause”.
Former First Minister Arlene Foster reminisced on the “happy memories” she shared with Rev Smyth.
Lord Peter Weir, a former Education Minister, said he was “a staunch unionist and Orangeman, dedicated public servant and man of conviction”.
“He was prepared to be a political representative at a time when it literally risked his life,” he added.
Rev Martin Smyth in 2014 and in 1970.
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Rev Smyth’s views were conservative and often hardline.
He resigned his ministry and was elected to Parliament in the 1982 by-election following the murder of Rev Bradford.
Rev Bradford (40) and a 29-year-old caretaker, Ken Campbell, were shot dead during a constituency clinic at Finaghy Community Centre.
In a lengthy political career, Rev Smyth was an unsuccessful candidate for the UUP leadership in 1995 after the resignation of Lord Molyneaux, finishing fourth to the winner, David Trimble.
In 2000, Rev Smyth unsuccessfully attempted to oust Mr Trimble as leader on an anti-agreement platform.
In January 2005, he announced he would be stepping down from Westminster at the next election to spend more time with his wife.
Alasdair McDonnell took the South Belfast seat for the SDLP in the 2005 election.