During the 1760s Lightoler developed a considerable practice as an architect. He was engaged on five houses, six churches and five industrial projects. His most important works in this capacity were Platt Hall (a substantial country house in the manner of John Carr), the Octagon Chapel at Bath and Bidston Hall in Cheshire.  He designed the churches of St Paul and St John in Liverpool, both domed buildings of considerable merit, and the church of St Mary in Manchester.

Although more law-abiding than his jailbird brother, it seems Lightoler was "prepared to use unorthodox, even underhand methods to gain a commission". In 1761 he began construction of a new factory near Birmingham for Matthew Boulton to be built by William Wyatt; by 1763 Wyatt had dismissed Lightoler as architect, describing him as "the greatest Lyar I ever yet met with for during the half hour he stay'd with me I verily believe he did not say one true thing". 

Lightoler was at the height of his career when he designed the grand Palladian stable block for William Constable. Lightoler’s design and that presented by prominent architect John Carr of York at the same time are still held at the house today. William very likely chose Lightoler’s plans because of the architect’s adaptability and his ability to design in the Palladian and New Classical style. As William was an astute man who liked looking after the pennies, however, Lightoler’s very competitive price of only £63 for his drawings and attendance at the Hall may also have been a key factor in undercutting Carr’s work. As Carr was in fact the more prestigious of the two, William may even have favoured Lightoler as being the architect he could influence most - the plans show several alterations, which were very possibly made at William's behest. No notable qualified professional architect of the day would have seen need for modification to their work.

Lightoler died in 1769, before the stable block was completed, and was buried in the graveyard of the prestigious church of St Paul, Liverpool - the church he had designed to compete with the church of St Paul in London.

Thomas Atkinson (1729-1798) of York was commissioned to complete the stable block. Atkinson interestingly converted to Catholicism in order to obtain contracts from Catholic gentry, a path which Lightoler (for all his finagling for commissions) never seems to have resorted to.