Mansel was appointed a writer in the British East India Company's service on 30 April 1826.
From 1844 to 1849 he was on furlough, and on his return to India was appointed a member of the board of administration for the affairs of the Punjáb, under the presidency of Sir Henry Montgomery Lawrence.
In November 1850 he was gazetted the resident at Nagpur, where he remained till 1855, when he retired upon the East India Company's annuity fund.
He is chiefly remembered as the junior member of the board to which was entrusted the administration and reorganisation of the Punjáb after its annexation.
He died at 7 Mills Terrace, West Brighton, England, on 19 November 1886.