The aircraft was designed in response to a Polish Air Force requirement of 1946 for a trainer to replace the Soviet UT-2, which was obsolete. The new aircraft was designed in 1947 in the LWD (Lotnicze Warsztaty Doświadczalne - Aircraft Experimental Workshops) - the first Polish post-war construction bureau. The chief designer was Tadeusz Sołtyk. A prototype named the LWD Junak, later the Junak 1, was flown on February 22, 1948 (its name means "brave young man"). The entire design was Polish, except for the engine, which was a license-built Soviet radial, the Shvetsov M-11D (93 kW, 125 hp).
After tests, an improved variant, the Junak 2 was flown on July 12, 1949. Notable changes from the Junak 1 included the cockpit being moved forward, the fin being increased in area, a more powerful M-11FR engine (118 kW, 160 hp) was fitted and the massive landing gear covers were deleted. The plane's handling improved. The LWD team disbanded in 1950 and Junak 2 development was continued by the CSS workshops in Warsaw. After further improvements the prototype was designated the Junak-2bis, but finally entered production in 1951 as the Junak-2. Tadeusz Sołtyk was given a State Award in 1952 for the design. From 1951 to 1954, 105 Junak 2s were produced in the WSK-Okęcie in Warsaw (the first 3 in the WSK-Mielec).
Tadeusz Sołtyk, then working in the Aviation Institute (Instytut Lotnictwa - IL) in Warsaw, proposed a Junak development with a bubble canopy, retractable landing gear and other improvements, designated the TS-7 Chwat, but it was not ordered by the authorities and remained on the drawing board. Instead, when the Polish Air Force was equipped with its first jet fighters, (the Yak-23 and MiG-15), there appeared to be a need for a trainer with a tricycle landing gear. Sołtyk designed a modified Junak with a fixed tricycle landing gear and other minor improvements. This plane entered production as the TS-9 Junak 3 ("TS" standing for the designers initials), after having first flown on August 7, 1953. The new plane was heavier, its maximum speed dropped from 223 km/h (139 mph) to 205 km/h (128 mph). Between 1953 and 1956, 146 Junak 3s were produced in WSK Warszawa-Okęcie.
Along with the Junak 1, the LWD developed a civilian trainer and aerobatics variant, the LWD Zuch. Only 5 Zuch 2s were built in 1950, powered by a 116 hp Bramo Sh 14 radial engine.
The Junak was the first aircraft mass-produced in Poland after World War II, the Polish aviation industry having been annihilated. Despite not being particularly modern, it was a stable and easy-to-handle aircraft, with an uncomfortable cockpit being one of its few flaws. On the other hand, it was considered a difficult aircraft to learn to fly, because a student in a rear cockpit had worse view. All models of Junak are generally referred to as LWD Junak or WSK Junak, while the designation TS-9 is not commonly used. The designation IL Junak 3 sometimes appears in books.