[2] On completion of his schooling Jeffcott studied law at the Rolls Office, under John McHutchin, and was called to the Manx Bar on May 9, 1839.

[2] For a considerable number of years Jeffcott possessed the largest legal practice in the south of the Isle of Man, and he earned a reputation as a sound and trustworthy lawyer.

[2] Following the resignation from the chief magistracy of James Gell in 1865, Jeffcott was appointed High Bailiff of Castletown by the Isle of Man's Lieutenant Governor, Henry Loch.

At this time the House of Keys met in the ancient capital of the Isle of Man, Castletown, and was a self elected body.

[2] Although he was not the direct driving force, Jeffcott had a substantial influence in the moulding of legislation at a critical period in the history of the Isle of Man, notably in the reform movement which led to the settlement of 1866.

[2][4] His elder son, also named John Jeffcott, became an engineer in Vancouver, British Columbia, in the service of the Pacific Steam Navigation Company.

[6] Another work of eminence was his delineation of the character and description of the unique Meayll Stone Circle on Mull Hill and in addition he was highly knowledgeable regarding other historic sites particularly those on Cronk ny Arrey Laa.

It would appear Jeffcott fell on hard times, for in October 1885 he and his wife entered into a deed which assigned and conveyed their real estate to trustees, to be sold to satisfy charges upon it.