The son of Richard Brownlow and Katharine Page, he was educated at St Mary Hall, Oxford, where he graduated with a Bachelor of Arts in 1610 or 1611. In 1617, Brownlow was called to the Bar by the Inner Temple. Created a Baronet, of Humby in the County of Lincoln on 27 June 1641, he was a Parliamentarian during the English Civil War. From 1653, Brownlow was Member of Parliament (MP) for Lincolnshire.
Around 1624, he married Elizabeth Duncombe, daughter of William Duncombe. They had a daughter and a son, Richard Brownlow.