After his sixth voyage, having served as fifth, third, and first mate successively, he obtained, in 1809 (when less than twenty-eight years of age), the command of Lady Lushington.
He found himself in a context where reforming ideas were up in the air; and eventually became a significant rival to John Thomas Becher of Southwell.
At Southwell, too, he instituted a workhouse school, to which children of labourers with large families and applying for relief were admitted and kept during the day, returning to their parents at night.
[1] Early in 1823, Nicholls was consulted by George Barrow about the Gloucester and Berkeley Canal, at that time incomplete and lacking funds.
Among their joint schemes was the plan of the English and Bristol Channels Ship Canal, in favour of which in December 1824 he and Telford reported.
[1] At this period Nicholls was asked by Alexander Baring to go out and report on the feasibility of a Panama Ship Canal, but declined on account of the climate.
It was proposed that Nicholls should go out to organise branches at Bombay, Madras, Calcutta, Singapore, and Canton, and that a post should be reserved for him at Liverpool or London on his return.
The Poor Law Amendment Act 1834 was passed the same year, and in August Nicholls was appointed one of the three commissioners entrusted with its administration, the other two being Thomas Frankland Lewis (later succeeded by his son George Cornewall Lewis) and John Shaw-Lefevre (later succeeded by Edmund Head); Edwin Chadwick was appointed secretary.
The question of the Irish poor law in the meantime became urgent; no feasible scheme was forthcoming till 1836, when Nicholls submitted to Lord John Russell, by request, certain "suggestions" on the subject.
He was also, early in 1838, sent by the government to the Netherlands and Belgium to make examination of the mode of administering relief and the condition of the poorer classes in those countries.
Upon the passing of the Irish act he was requested by government to superintend the early stages of its introduction, and he accordingly proceeded in September 1838 to Ireland, residing, with his wife and children, at Lis-an-iskea, Blackrock, Dublin.
The Irish poor law and its administration were subjected to violent criticism, both in and out of parliament; but the bitterest opponents bore testimony to Nicholls's character and ability.
Between 1848 and 1857 he was consulted three times by persons making inquiries on behalf of the French government, and once by Professor Kries of Breslau, the object in all four cases being to obtain materials for proposed poor law legislation on the continent.
He continued to take an active part in the affairs of the Birmingham Canal, and he was also a working member of the committee of the Rock Life Assurance Company.
Willink A History of the English Poor Law (1904) Nicholas married on 6 July 1813 Harriet, daughter of Brough Maltby of Southwell, Nottinghamshire.