This active lawyer, who numbered both Surrey landowners and city merchants among his clients, was probably the son of Robert Solas, a resident of Southwark and collector of the local lay subsidy there in 1380. The Thomas Solas with whom he was returned to Parliament in 1393 may well have been his brother, for the family then enjoyed considerable influence in the borough. John’s legal career had evidently begun well before the Trinity term of 1384, when he became a clerk of the King’s bench with particular responsibility for enrolling the records for Surrey and Sussex. He also practiced extensively as an attorney, and first appears in this capacity at the local assizes in March 1390. In the following March he himself was being sued for menaces by a London fishmonger, one of many persons to experience the full effects of his uncertain temper. Another was the poet, John Gower, who lived in Southwark and took him to law, in 1405, for similar acts of violence. On this occasion William Kirton, his colleague in the Parliament of 1414 (Nov.), helped him to raise the necessary sureties of £200.
Not surprisingly, Solas established himself as a man of some consequence in Southwark, not merely because of his professional status, but also as a result of his shrewd investment in the property market. In June 1397 he paid £20 for a messuage, two shops and two acres of land there, having raised part of the money through an earlier sale of a toft and farmland in the Newington area. Several years later, in 1414, he and his feoffees successfully established their title to another three messuages in Southwark, which were then being leased by him to tenants at a substantial annual rent. Solas died a wealthy man. His will, drawn up on 12 July 1418 and proved ten days later, lists numerous bequests of clothing and money to his friends and servants, as well as a gift of £5 to St. George’s church, Southwark, where he chose to be buried.