Mr Blair was born at Kingsmills, Co. Tyrone. The place were he was born is called Blairs Corner and is almost beside the Kingsmills Gospel Hall. Attending meetings conducted by Messrs Campbell and Matthews, who were true pioneers, he was led to see his condition and need of Christ as his Saviour. After some time of deep soul trouble, on 12th July, 1880, while reading Romans 5.6, he was saved. Almost at once he gave himself wholeheartedly to the things of God, taking an interest in the gospel, and two years later went forth to tell it out. In this he was manifestly helped of God and all who knew him and heard him preach, believed that John "was a man sent from God".
He laboured for a time in the north of Ireland with signs following his plain, solemn preaching. Sinners were awakened and saved, and Gods people led to devote themselves to the things of God. An outstanding evidence of the weight and lasting effects of his preaching was seen when an unsaved woman was heard to say, "I could die happy if I had not heard John Blair preach". Though she was not saved, his words had reached her heart and remained with her.
He went to the USA in the spring of 1891. All that season he laboured in tent work at New Bedford and Falls River, Massachusetts, and in the autumn went to New Brunswick, Canada. He had an unsaved sister living in Independence, Iowa, about whose spiritual condition he was deeply concerned. After getting no satisfaction from correspondence, he decided to visit her. At that time he had no money but was assured that it was the mind of the Lord that he should go. He started for the railway and took his place in the line before the ticket window. He was third in the line when a brother appeared and handed him an envelope remarking, "I have hunted for you all day". The envelope contained the exact amount of the fare. He arrived in Iowa on 30th November, 1891. These godly men trusted God in a remarkable way and He never failed them.
He was the first to bring the gospel to that part of Iowa, holding meetings in houses and later in a school building, and some were saved including his sister. He returned in 1893 and 1895 holding meetings in the school and in church buildings in Dunkerton and Waterloo. A Mr and Mrs Dunkerton, who were saved among the Free Methodists, were greatly helped by his ministry and it was in their home that they first met to "remember the Lord" in 1893. The work thus begun in this simple way prospered, and God continued to bless; there are now many assemblies in Iowa. His last visit there was in 1922 when he had meetings in Jessop and Stout in company with Mr O Smith, God again working, and many were saved including Mr Blairs nephew. He travelled extensively in the USA and Canada as well as making three visits to New Zealand. His faithful gospel preaching and upbuilding ministry caused him to be held in high esteem wherever he went.
Mr W J McClure wrote to Mr F Ferguson about him after he died and said, "He was a godly man, spending more time alone with God that any man I knew, unless it was the late Andrew Frazer, who he in many respects resembled. He could not preach if he had not the sense of Gods presence with him, and as a result he brought more of Gods presence into the meetings than half a dozen "wordy preachers"- now too common. For this very reason his going is a distinct loss to the assemblies - we are in more need of such men as dear John Blair. May God raise them up". In later years his health could not stand the cold and he settled in Los Angeles, California, where on 10th June, 1929 he ceased from his labours and entered into the Lords presence. Large numbers, some from great distances, attended his funeral. Tributes and respect were shown to an honoured servant of Christ. Messrs Becker and Greer gave words of admonition and comfort to all present.