Owen was born about 1711, a nephew of James Owen (1654–1706) and Charles Owen. He is generally said to have been the son of their eldest brother, David Owen (died 7 October 1710, aged 59), minister of Henllan, Carmarthenshire, and may have been a posthumous son.
Josiah Owen was educated by his uncle Charles Owen at Warrington.
His first settlement as minister was at Bridgnorth in Shropshire (after 1729), which he left in 1735. He then ministered for short periods at Walsall, and at Stone, Staffordshire. Some time after June 1740 Owen became minister of Blackwater Street Chapel, Rochdale, Lancashire.
His ministry was immediately successful, and his chapel was enlarged in 1743.
Owen"s ministry at Rochdale ended on 14 June 1752.
He came to prominence with the 1745 Jacobite Rebellion, as a political and religious writer against Jacobitism.
