Sir James Lowther, 4th Baronet, FRS (1673 – 2 January 1755) was an English landowner, politician and industrialist. He obtained immense wealth from coal mines in northern England, which he extensively developed and modernised.
He was baptised on 5 August 1673 at St Giles in the Fields, London, the second son of Sir John Lowther, 2nd Baronet and Jane Leigh. Educated privately in London, he attended Queen's College, Oxford and the Middle Temple.
In 1694, he was returned as Member of Parliament for Carlisle, a seat he held until 1702. He also served on the Board of Ordnance from 1696 until 1708, when he re-entered Parliament for Cumberland. This seat he held until 1722; in 1723, he was returned for Appleby, but in 1727 was MP for Cumberland again, and would be so for the rest of his life. Politically, Lowther was a Whig, but with little interest in national affairs; his Parliamentary activity was primarily directed towards promoting local interests in Cumbria. He was sworn a Privy Counsellor in 1714.
In 1706, he inherited the family estates upon the death of his father, his elder brother Christopher having been disinherited as a spendthrift. The principal wealth of the estates was in collieries, and he made extensive investments to improve and extend his holdings. To facilitate the coal trade, he made improvements to the harbour facilities at Whitehaven, which became a major coal port for shipping to Dublin and elsewhere. Lowther also sought to promote iron manufacture in the area, and develop Whitehaven as a planned town, an enterprise first begun by his father in the 1680s. He succeeded his brother in the baronetcy in 1731.