In 1798 he became an audit clerk in London and was, due to assistance from William Pitt the Younger, appointed collector of customs in Halifax, Nova Scotia.
In 1810, Jeffery was appointed to the Nova Scotia Council and supported Uniacke's high church Toryism.
In 1828 and again in 1834, Jeffrey was Acting Lieutenant Governor of Nova Scotia pending the arrival of permanent viceroys.
to preserve the peace and promote the welfare of the country.” When the Legislative and Executive Council of Nova Scotia were split into separate bodies in 1838, Jeffery was appointed to the latter institution.
In 1815, Jeffrey was given responsibility for the settlement of Black refugees following the War of 1812 and settled some families on his lands by the Shubenacadie River.