He was JP for Shropshire from about 1598 and was collector for the loan in 1598. He was active in campaigns against recusancy. In 1598 he helped search for the escaped Jesuit priest John Gerard and in the following year served on a commission with his brother-in-law, the Warwickshire MP Edward Greville, to search out recusants' goods and lands. In 1600 he was assessed, as of Shropshire, to furnish one horse for service in Ireland. This was for the expedition of Robert Devereux, 2nd Earl of Essex. At least by the time of his imprisonment, Bromley had been closely associated with Essex, offering to "do him service" in a letter he wrote jointly with his brother-in-law, Sir John Scott. The more collegial political arrangement of the previous two decades had been superseded by intense factional struggle, between Essex and Robert Cecil, with the queen herself increasingly indecisive and remote. It was a struggle to control royal policy between the queen's favourite and her most trusted minister, in which the latter had the major political and institutional advantages, including continuous direct access to Elizabeth and use of the powerful government intelligence network. Essex inherited the following of many individuals and families who had supported Leicester, including the Sidneys and regional Puritan politicians like Bromley. By promoting his image as a Protestant hero and patronising Puritan clergy, as well as taking up the cause of James VI, he hoped to appeal to wide circles of support in London and in Parliament. However, as recent evaluations make clear, Essex also had a strong cultural appeal for men like Bromley: more than a mere playboy, he projected himself as a cultivated nobleman, with a following that was strongly focussed on classical learning and martial honour. In July 1600, Bromley wrote to Henry Cuff, one of the militant, classically educated men in the earl's household, expressing his whole-hearted commitment, in a letter that was intercepted and copied for Cecil:  Bromley was also tied to Essex also through family and regional networks. His brother-in-law John Lyttelton was MP for Worcestershire and allied to his distant relative Edward Littleton, who managed political matters for Essex in neighbouring Staffordshire, which he regarded as his "own country", and had his seat at Chartley Castle. However, Lyttelton was well known to have Catholic sympathies. An important part of the cement holding the Littletons of both counties in the alliance around Essex was a shared antipathy to Edward Sutton, 5th Baron Dudley, a reprobate regional magnate, also of Catholic sympathies, who attempted to disrupt the election of MPs loyal to Essex.