John Krebs was born in Hagerstown, Maryland on May 6, 1804, the son of William and Ann Adamson Krebs. The senior Krebs was a merchant and postmaster in the town and John received his early education there before he went to work as a clerk in his father's post office. His father died in 1822 and soon after he became determined to join the Presbyterian Church. After instruction at the local academy, he entered Dickinson College in February 1825. Krebs graduated in the class of 1827 with high honors and commenced pastoral studies under the Rev. George Duffield of Carlisle. He also received an appointment at the Dickinson Preparatory School and taught there between 1827 and 1829. By 1829 he had been licensed to preach in the Carlisle Presbytery, but, in May 1830, he briefly entered Princeton Theological Seminary. As soon as November, 1830, he had been formally ordained and taken up a post as pastor of the Rutgers Street Church in New York City.
Krebs' qualities attracted the leaders of the church and he was appointed as the permanent clerk of the General Assembly of the Presbyterian Church in 1837. He filled this post until 1845 when he served as Moderator of the General Assembly. By then he had been awarded a doctorate of divinity from his alma mater, in 1841, and had been a director of the Princeton Seminary; he later became president of the seminary board in 1866. Also in 1866, he was chairman of the committee charged with the reunion of the Old and New Schools in the north. This was an interesting appointment considering his early education with the firebrand, "new light" revivalist Duffield. He had to turn over much of this last work to others on the committee, however, as his health was beginning to fail precipitously.
In October 7, 1830 Krebs married Sarah Holmes of Carlisle and the couple had two children before her death in February 1837. He was married for the second time to Ellen Chambers of Newburg, New York and she died in 1863. His own health having failed soon after, John Michael Krebs died at his home in New York City on September 30, 1867 at the age of sixty-three.