Barbon was responsible for joining the city to the seat of government at Westminster for the first time as a result of developments along the Strand, Bloomsbury, St Giles and Holborn.

[3][7] On 11 June 1684, Barbon's expansionary speculation brought him and his building tradesmen into conflict with lawyers based at Gray's Inn.

[1][3] "He was unique in the unscrupulousness and brazenness of his business tactics" and his contemporary Roger North, who studied his dealings and interviewed him on the subject, called him "an exquisite mob master" in recognition of his ability to manipulate people to carry out his schemes.

Largely in order to take advantage of Parliamentary privilege and thus gain immunity from prosecution by his creditors[3] he bought a number of burgages[14] in the rotten borough of Bramber in Sussex, which enabled him to be elected one of its Members of Parliament in 1690 and 1695.

[3][15] His works, especially A Discourse of Trade (written in 1690), influenced and drew praise from 20th-century economists such as John Maynard Keynes (in The General Theory of Employment, Interest and Money)[16] and Joseph Schumpeter.

[17] He was one of several late 17th-century economic, social and political theorists with a medical education background; contemporaries included Benjamin Worsley, Hugh Chamberlen, William Petty and John Locke.

[21] Such criticism of mercantilism—the view that a country's prosperity can be measured by its stock of bullion—helped to lay the foundation for classical economics, and was unusual at the time.

Along with John Locke, with whom he debated his theories, Barbon was one of the first theorists to argue that money's value was principally symbolic and that its main function was to assist trade.

He also advocated the use of paper and credit money, and postulated the reduction of interest rates, which he thought impeded the growth in manufacturing and trade.

[21][24] He discussed these issues in his 1696 pamphlet, which also considered the effects of the Recoinage of that year, in which the Royal Mint recalled large quantities of silver coins, melted them down and reminted them, resulting in a temporary fall in the supply of money.

[3] Despite the importance of some of his theories, Barbon's work (especially A Discourse of Trade) has been criticised for an excess of "definition and classification" instead of analysis and a disjointed style which lacked rigour.

By the time of his death, Barbon had built or financed developments to the value of £200,000 (£33 million as of 2025)[13] according to Sir John Lowther, 1st Viscount Lonsdale.