After attending public school in Brechin, he was accepted to University of Dundee (which was then part of the University of St Andrews). He graduated with a BSc in engineering in 1912, and was offered an assistantship by Professor William Peddie. It Peddie who encouraged him to study radio, or "wireless telegraphy" as it was then known.
In 1915 Watson-Watt wanted a job with the War Office, but nothing obvious was available in communications. Instead he joined the Meteorological Office, who were interested in his ideas on the use of radio for the detection of thunderstorms. Lightning gives off a radio signal as it ionizes the air, and he planned on detecting this signal in order to warn pilots of approaching thunderstorms.
His early experiments were successful in detecting the signal, and he quickly proved to be able to do so at long ranges. Two problems remained however. The first was locating the signal, and thus the direction to the storm. This was solved with the use of a directional antenna, which could be manually turned to maximize (or minimize) the signal, thus "pointing" to the storm. Once this was solved the equally difficult problem of actually seeing the fleeting signal became obvious, which he solved with the use of a cathode-ray oscilloscopes with a long-lasting phosphor. Such a system represented the majority of a complete radar system, and was in use as early as 1923.
At first he worked at a site in Farnborough, but in 1924 a new research centre was set up at Ditton Park near Slough (to the west of London) where he moved. The National Physical Laboratory (NPL) also had a research station there, and in 1927 they were amalgamated as the Radio Research Station, with Watson-Watt in charge. After a further re-organisation in 1933, Watson-Watt became Superintendent of the Radio Department of NPL in Teddington.
In 1933 the Air Ministry had recently set up a committee to advance the state of the art of air defence in the UK. In World War I the Germans had used Zeppelins as long-range bombers over London, and attempts to attack them by aircraft had proven to be failures (although anti-aircraft batteries did well). Even though the Zeppelins were 100s of metres long and moved at only 100 kilometers an hour, in the 20 raids where fighters were launched, they only saw the target three times, and were never able to attack.
With modern bombers able to approach from altitudes where the anti-aircraft guns were unable to reach, statistics like these were frightening. Worse, with the enemy airfields only 20 minutes away, the bombers would have dropped their bombs and be returning to base before the intercepting fighters could get to altitude. The only solution would be to have standing patrols of fighters in the air at all times, but with the limited cruising time of a fighter this would require a gigantic standing force. Something needed to be done.
It was at about this time that Nazi Germany claimed to have a "death-ray" which used radio waves, and claimed it was capable of destroying towns, cities and people. The committee's chair, H.E. Wimperis, visited Watson-Watt at Teddington in 1934, asking about the possibility of building their own version of such a death-ray, specifically for use against aircraft. Watson-Watt quickly returned a calculation showing that such a device was basically impossible to construct, and fears of a Nazi version soon vanished. However he also mentioned in the same analysis "Meanwhile attention is being turned to the still difficult, but less unpromising, problem of radio detection and numerical considerations on the method of detection by reflected radio waves will be submitted when required."
On February 12, 1935, Watson-Watt sent a memo of the proposed system to the Air Ministry, entitled Detection and location of aircraft by radio methods. Although not as exciting as a death-ray, the concept clearly had amazing potential and Watson-Watt was promptly asked for a demonstration. This was ready by February 26, and consisted of two receivering antennas located about ten kilometers away from one of the BBC's shortwave broadcast antennas at Daventry. Signals travelling directly from the station were filtered out, and a Heyford bomber flown around the site. Such was the secrecy that only three people witnessed the test, Watson-Watt, his assistant Arnold Wilkins, and a single member of the committee, A.P. Rowe. The demonstration was a success: on several occasions a clear signal was seen from the bomber.
Only two weeks later Wilkins left Teddington with a small party to start further research at Orfordness. By June they were detecting aircraft at 27 kilometers, which was enough to stop all work on competing sound-based detection systems. By the end of the year the range was up to 100 kilometers, at which point plans were made in December to set up five stations covering the approaches to London.
One of these stations was to be located on the coast near Orfordness, and Bawdsey Research Station was set up there to become the main research centre for all radar research. In early tests with the first of what would later be known as Chain Home, it was clear that one of the main problems would be reporting the positions so that Fighter Command could attack the targets properly. Watson-Watt immediately attacked this problem, and set up the system of having several layers of reporting that were eventually sent to a single large room for mapping. Observers watching the maps would then tell the fighter groups what to do.
By 1937 the first three stations were ready, and his new reporting system put to the test. The results were clearly successful and an immediate order for an additional 20 stations was sent out. By the start of World War II 19 were ready to play a key part in the Battle of Britain, and by the end of the war over 50 had been built.
Even as early as 1936 it was realized that the Luftwaffe would turn to night bombing if the day campaign did not go well, and Watson-Watt had put another of the original Teddington group, E.G. Bowen, in charge of developing a radar that could be carried by a fighter. Night time visual detection of a bomber was good to about 300m, and the existing CH systems simply didn't have the accuracy needed to get the fighters that close.
Bowen decided that a airborne radar should not exceed 200 pounds in weight, eight cubic feet in volume, and require no more than 500 watts of power. To reduce the drag of the antennas the operating wavelength could not be much greater than one meter, difficult for the day's electronics. Nevertheless such a system was perfected by 1940, and were instrumental in eventually ending "The Blitz" of 1941.
In July 1938 Watson-Watt left Bawdsey Manor and took up the post of Director of Communications Development (DCD-RAE). In 1939 Sir George Lee took over the job of DCD, and Watson-Watt became Scientific Advisor on Telecommunications (SAT) to the Air Ministry, travelling to the USA in 1941 in order to get radar research started there.
His contributions to the war effort were so overwhelming that he was knighted in 1942. In 1952 he was awarded £50,000 by the British government for his contributions in the development of radar. He spent much of the post-war era in Canada, and later the USA, where he published Three Steps to Victory in 1958. He returned to Scotland in the 1960s and died in Inverness.