The progenitor of the Baron was the Beechcraft 95 Travel Air, which incorporated the fuselage of the Bonanza and the tail control surfaces of the T-34 Mentor military trainer. To create the new airplane, Beech replaced the Travel Air's tail with that of the Beechcraft Debonair, streamlined the engine nacelles and rechristened the aircraft as the Baron.

The early Baron 55, 55A and 55B were fitted with Continental IO470 260 hp (194 kW) engines and had gross weights of 4880 to 5100 lb (2,200 to 2,300 kg). These had a typical cruise speed of 190 knots (350 km/h) at 7000 ft (2100 m), and came with 116 or 136 US gallon (440 or 515 L) fuel tanks.

The 55C, 55D and 55E models had an increased cruise speed of 200 kt (370 km/h) due to the bigger Continental IO520 285 hp (213 kW) engines. The gross weights of these later models increased to 5300 lb (2400 kg). They were about a foot (0.3 m) longer than the 55B Barons, and came with 136 or 166 US gallon (515 or 628 L) fuel tanks. Model 55 Barons were produced from 1961 to 1983, and some 3,155 were produced.

Beech also produced, in limited quantities, a 56 model Baron, which featured the short fuselage of the 55 series Baron with massive TIO-541 Lycoming engines which were turbocharged and produced 380 hp each. At the time, it was the fastest Beech aircraft, rivaling even the early King-Airs offered by Beech at the time.

Introduced in 1970, the more powerful Baron 58 has club seating, double aft doors, and a gross weight of 5400–5500 lb (2450–2500 kg), and is fitted with either the Continental IO520 or IO550 300 hp (224 kW) engine. The Baron 58 can cruise at 200 knots (370 km/h) at 7000 ft (2100 m), and is equipped with either 166 or 190 US gallon (628 or 719 L) fuel tanks.

In 1976, the turbocharged Baron 58TC and pressurized Baron 58P were introduced. These variants were powered by Continental TIO520 turbocharged engines of 310–325 hp (230–240 kW) and had an increased 6100–6200 lb (about 2800 kg) gross weight, and were certified under FAR23 with a new type certificate. The Baron 58P/58TC models were capable of cruising at 200 knots (370 km/h) at 8000 ft (2400 m) and 220 knots (410 km/h) at 20000 ft (6100 m), and were typically equipped with 190 US gallon (719 L) fuel tanks.

A big change in panel/system layout on 58/58TC/58P occurred in 1984, including relocating throttle, gear, flap, propeller and mixture controls to industry-standard positions. Although the turbocharged 58TC/58P variants were discontinued in 1985, the normally aspirated Baron 58 is still in production as of 2006.

The T-42A Cochise is a military version of the Baron used by the United States Army as an instrument training aircraft. By 1993, the Army's remaining T-42 aircraft had been transferred to the Army Reserve and the National Guard and were no longer in standard use.