David Deas was born at Falkland in September 1807 son of Francis Deas, provost of Falkland, Fife and Margaret, daughter of David Moyes. He was educated at the high school and the University of Edinburgh, and having become a licentiate of the Royal College of Surgeons of Edinburgh in 1827, entered the Royal Navy 7 June 1828 as an assistant-surgeon. 
He was appointed assistant surgeon on the Dee steamer in 1834
He was appointed Surgeon to the Hydra in 1839.
David Deas was on the List of Surgeons of the Royal Navy who were fit for service in 1841.
Surgeon Superintendent Lord Petra 1843
He was appointed Surgeon Superintendent on the Lord Petra in 1843 (to VDL). He kept a medical journal from 17th June to 15th November 1843.
He was appointed Surgeon to the Amazon in 1844  and to the Southampton in 1848
In 1854 he was appointed Deputy Inspector to the Britannia.
In November 1854 he was Deputy Medical Inspector of Fleets when he signed a roll of the killed and wounded in the Siege of Sebastopol 
In 1855 he was promoted from Deputy-Inspector of Hospitals to Inspector of Hospitals and appointed to Royal Albert, flag ship of Rear Admiral Sir Edmund Lyons on the Black Sea station 
He was awarded Order of the Bath in 1856  and Order of the Legion of Honor in July 1856.
He was appointed Chief Surgeon of the Fleet in 1857
He was appointed to succeed Dr. Nisbet in medical charge of Haslar Hospital in March 1861
He is listed in the Medical Register of 1865 -
Inspector General of Hospital and Fleets R.N.,
Qualifications Lic. Royal College of Surgeons, Edinburgh 1827.
In 1868 he attended the Portsmouth Medico-Chirurgical Society where he made observations on yellow fever in the West Indies (Medical Times and Gazette 1868)
On 31st July 1860 he was married at Hollycot, Lasswade to Margaret, youngest daughter of William Hepburn Esq., . A son was born to the couple on 5th April 1862 at Haslar, Gosport.
The Blackburn Standard reported on 22 January 1876 that Sir David Deas, K.C.B., Inspector-General of Hospitals and Fleets died on Saturday in his 69th year at the residence of his brother Lord Deas, in Edinburgh.