Born: April 3, 1827, Iredell County, North Carolina.
Died: September 23, 1901, Kutztown, Pennsylvania.
Buried: Fairview Cemetery, Kutztown, Pennsylvania.
Sydney was the son of John and Sarah Harkey. He married twice, to Mary Jane Jenkins (May 16, 1848) and Susie Freeman (around 1872).
He grew up on a farm, and while he was still small boy, his family moved to Illinois.
He attended the Hillsboro Academy, and (1844–47) Pennsylvania College. He studied theology under his brother, Dr. Simeon W. Harkey.
He received his preaching license in Cumberland, Maryland, in 1848.
During his ministry, he served many congregations and parishes:
Harkey also served as an agent of Illinois University (1857); army chaplain (1862); professor at Augustana College and Theological Seminary (1868–70); secretary of the Lutheran Illinois Synod (1853–54); president of the Illinois Synod (1856–57 & 1858–60); president of the Synod of Illinois and Adjacent Lakes (1867–69); secretary of the General Council (1885–87); and president of the Reading Conference (1897–1900).