The broadcaster and writer was best known for a series of books on Syria that were widely respected, although critics said he was too supportive of the Assad regime.
Seale died of brain cancer in London, having been diagnosed last June, said the Observer, the British Sunday paper for which he was once the Beirut correspondent.
As Beirut correspondent, he replaced his friend Kim Philby, the British MI6 spy and traitor who defected to Moscow in 1963.
His "Struggle" trilogy also included "The Struggle for Syria" and the "The Struggle for Arab Independence."
Also Read
Journalist Tim Llewellyn wrote in his Observer obituary that "Seale's familiarity with Syria and its leaders engendered much criticism of him, and suspicion that he was an apologist, mostly from people who were parti pris themselves, especially the Lebanese establishment, or those who chose to confuse explanation with exoneration."
The British ambassador to Lebanon, Tom Fletcher, said Seale was a "wise, curious, mischievous lion of Levant history."
"Patrick Seale knew the Middle East inside out. But his wisdom was that he also knew how much he didn't know, and was furiously curious," Fletcher wrote on Twitter.
Seale was born in Belfast, Northern Ireland, in 1930 to a biblical scholar father and a Tunisian-Italian midwife mother.
Shortly after his birth, the family moved to Syria where they were missionaries, and his time growing up in the region fuelled a life-long fascination.
He was schooled in Damascus and England before going to Oxford University. He then moved to Beirut where he started freelancing.