In 1863, he was elected the third chairman of the Hong Kong General Chamber of Commerce. He played a leading role in the establishment of the Hongkong and Shanghai Banking Company and was one of the proprietors when the bank was incorporated in 1866. He returned to London in 1864 with a fortune of about £800,000, which he amassed in China, and joined the formation of the Blakely Ordnance Company and became the chairman of the firm with the capital of £120 000.
John Dent was appointed an unofficial Justice of the Peace in 1844.
He was reappointed to the Legislative Council in 1866. He resigned in 1867 after his firm went bankrupt in 1867 and was replaced by Phineas Ryrie.
Dent was also appointed consul for the Kingdom of Sardinia and later the Kingdom of Italy in Hong Kong from 1858 to 1867. Dent & Company went bankrupt in 1867 during the worldwide financial crisis which originated in 1866 in London.
They suffered a loss of no less than £200,000 by the malversations of a Portuguese clerk in their employment at Shanghai who was sentenced to seven years imprisonment.
The petition for adjudication of bankruptcy was filed in the Supreme Court of Hong Kong on 29 June 1867. Dent had to removed his headquarters in Shanghai and sold the Dent Building to the Hong Kong Hotel Company
The clock-tower at the end of Pedder Street and the entrance to Queen"s Road in Central, Hong Kong, erected by public subscription in 1862, was at the suggestion of John Dent, whose original design had to be stripped of its original decorative features, owing to the waning enthusiasm of the community. John Dent also donated a fountain at the entrance of the old City Hall.
In 1870, Dent recommenced business as Dent & Company in Shanghai in the premises previously occupied by his old firm.
In April 1871 he became the Chairman of the Shanghai Municipal Council and served in that position until January 1873.
In 1857, he was appointed member of the Legislative Council of Hong Kong.