Browne was left the manor of Lenham, Kent by his father, an outlying property purchased by his grandfather, the 2nd Viscount, and which he disposed of soon after he inherited the title from his brother.
Montagu inherited the peerage in April 1708, but he was barred from the Lords by his Catholicism. His name appeared on one parliamentary list, of those voting on Sacheverell’s guilt in March 1710, but this was to note that he was a Catholic. It was probably soon after he assumed the viscountcy, that Montagu petitioned the queen for permission for his son, Anthony Browne†, the future 6th Viscount Montagu, to return to England, he ‘having been formerly in France, has for these last three years constantly resided at the duke of Lorraine's court at Luneville.’ Now he wanted to come home and had reached Rotterdam by using a pass from John Churchill, duke of Marlborough.
Montagu seems to have taken no role in the politics of Midhurst, possibly because he was not in possession of Cowdray House and Park, in which the dowager retained a life interest. His lack of interest in electioneering was made clear when in 1711 he sold several burgages to Charles Seymour, 6th duke of Somerset, who had been attempting to build up an interest in Midhurst since 1709. In 1709, as the only surviving trustee of the settlement for his Roper cousins (daughters of Christopher Roper, 5th Baron Teynham) he was negotiating with the commissioners of customs for the sale of land on the Isle of Grain.
Montagu’s inheritance was much circumscribed by the terms of his brother’s will and his debts which amounted to some £20,000 at his death.
Montagu challenged the other dispositions of his brother’s will, alleging that his sister-in-law had taken advantage of his brother’s fragile mental health in order to improve her personal financial position at the expense of the estate, including obtaining an annuity by means of a fraudulent codicil to his will. His charges were vigorously defended by the dowager viscountess and her husband, Sir George Maxwell, whom she had married in July 1710. An agreement between Montagu and his sister-in-law was drawn up in December 1710 but seems not to have been implemented.
Montagu died on 25 June 1717 and was succeeded by his son. He acquired posthumous fame in the story that he was responsible for the murder of a local priest and had to live out his years in hiding, a legend for which there is no contemporary evidence.
