Boswell had "adopted Thomas Sheridan as his mentor in Edinburgh in 1761, where Sheridan had come to give a series of lectures.". One of Boswell's friends at the time was West Digges, who had previously acted with Sheridan at the latter's Theatre Royal in Dublin, and it is likely that Digges had played some part in introducing the two.
The first mention of Sheridan in Boswell's London Journal is on November 28, 1762, when Boswell went to see him in London. On this occasion, Sheridan aired his newly found dislike for Dr. Johnson, as sometime earlier Sheridan had helped Johnson get a government pension. Now, Sheridan had got one as well, causing Johnson to exclaim "What!, has he got a pension? Then it is time for me to give up mine." - Sheridan apparently never forgave him. He also frequently criticized David Garrick. Boswell often went to see the Sheridans, especially during the early part of his stay in London.
On New Year's Eve, 1762, Boswell spent the evening at Sheridan's in the company of Mrs. Sheridan, Mrs. Cholmondeley, Capt. Jephson and Colonel Irwin. They had tea and listened to a reading of Frances Sheridan's new comedy The Discovery.
On January 18, 1763, Boswell visited the Sheridans to inquire about a prologue he had written for The Discovery. Apparently, Thomas Sheridan did not care much for Boswell's prologue, and a new one had been written by Mrs Sheridan herself. This caused Boswell to consider not seeing them again, but eventually, he reconsidered and decided to keep enjoying their company without caring about their opinions of him.
Following another visit on March 24, Boswell wrote in his journal:
I had called there a few minutes one day before; and both at that time and this I never mentioned The Discovery, which I thought the best way to pique them a little. This day he at last said to me, "You saw The Discovery only the first night?" "No more," said I. SHERIDAN. "O, then you did not see it to half the advantage." BOSWELL. "What, was it lightened?" (Garrick [had] said [to me], "We lightened it.") In this manner did I nettle them.
Paying Boswell back in kind, Sheridan said, during the same visit, about Andrew Erskine: "No, no, he is no poet. Neither you nor he are poets." Boswell noted in his journal that "[t]his was somewhat impertinent.", apparently unaware of the inherent irony of the situation, and his previous resolve not to care.
Sheridan also helped out Boswell when he had a gambling debt in 1761, and Boswell promised Sheridan that he wouldn't play cards again for 5 years, or at least that he wouldn't "lose more than three guineas in one sitting". Thomas Sheridan disappeared almost entirely from Boswell's writings during Boswell's tour of Europe, 1763-1766, although Boswell, in a memo on May 11, 1764, reminded himself to write to his former mentor.