The contrabass trombone is the lowest-pitched instrument in the trombone family of brass instruments. While modern instruments are pitched in 12-foot (12′) F with a single slide, the first practical contrabass trombones appeared in the mid-19th century built in 18′ B♭ an octave below the tenor trombone with a double slide. German opera composer Richard Wagner notably called for this instrument in his Der Ring des Nibelungen opera cycle in the 1870s, and contrabass trombone has since appeared occasionally in large orchestral works without becoming a permanent member of the modern orchestra.

Since the late 20th century, the double-slide contrabass has largely been supplanted by the less cumbersome bass-contrabass in F, a fourth below the B♭ tenor and bass trombones. In the 21st century the contrabass has enjoyed something of a revival, particularly in film and video game soundtracks.

The contrabass trombone first appeared in Renaissance music in the late 16th century. Bass trombones of the time were the quart-posaune pitched in E, or the quint-posaune in D, a fourth or fifth below the "common" tenor trombone in A. German music scholar Michael Praetorius, writing c. 1620, also describes two types of octav-posaune (lit. 'octave trombone'), one of which was a large sackbut built in A one octave below the tenor, with a very long slide and an extension handle to reach the lower positions. One such instrument survives, built in 18′ B♭. Praetorius called this double-length instrument very rare. Canadian trombonist and early music specialist Maximilien Brisson proposes the other type was a large-bore quint-posaune with an extra whole-tone crook, resulting in an instrument in C capable of playing down to G₁, the lowest open string of the G Violone. These large instruments were seldom used and generally unsatisfactory with players, being unwieldy and taxing to play.

The innovation that enabled a practical instrument was the double slide, first documented nearly two centuries later in 1816 by German writer and composer Gottfried Weber. He proposed that it would lend greater facility to the bass trombone, and described the idea of using two joined outer slides moving on four inner tubes, halving the distances between slide positions. Makers soon applied the double slide to bass trombones in F and E♭ that would normally require a slide handle to reach the longest positions. Newly invented models of contrabass trombone in low 16′ C and 18′ B♭ soon followed, and the first double-slide contrabass trombones were produced by Parisian maker Jean Hilaire Asté (known as Halary) in the 1830s.

In France, composer Georges Bizet called for contrabass trombone in his opera La Coutes du Roi de Thulé (1869), and in his completion in the same year of Noé, an unfinished opera by his father-in-law and French composer Fromental Halévy. Soon after, Wagner notably employed contrabass trombone in his Der Ring des Nibelungen, a cycle of four operas commonly known as the Ring cycle, writing a fourth trombone part to double on bass and contrabass trombone. For the première in 1876, Wagner commissioned a contrabass in 18′ B♭ from Berlin instrument maker Carl Wilhelm Moritz, who built it with a double slide. The double slide and the pitch one octave lower means this instrument has the same seven positions as the tenor trombone, and a range to the low E₁ in the "spear" motif in Das Rheingold:

In Britain in the 1860s, London instrument maker Boosey & Co. built a small number of "Basso Profundo" double-slide contrabass trombones in 16′ C. These were intended for use in British orchestras performing Wagner's operas, and one surviving instrument built in 1898 was named "King Kong" by players. At the turn of the 20th century, American instrument manufacturer C. G. Conn produced a small number of B♭ double-slide contrabass trombones.

Italian composers for much of the 19th century specified the cimbasso as the bass voice of the brass section, a confusing term which over time referred to an upright serpent, ophicleide, or early variants of the tuba. In preparation for the La Scala première of Aida in 1872, Italian opera composer Giuseppe Verdi expressed his displeasure about "that devilish bombardone" (referring to the tuba) as the bass of the trombone section, preferring a "trombone basso". In 1887 for Otello, Milan instrument maker Pelitti [it] produced the trombone basso Verdi (or sometimes, trombone contrabbasso Verdi), a valved contrabass trombone in low B♭. This instrument blended with the usual Italian trombone section of the time—three tenor valve trombones in B♭—and became the prototype for the modern cimbasso. Verdi and Italian opera composer Giacomo Puccini both wrote for this instrument in their later operas, although confusingly they often referred to it as simply trombone basso to distinguish it from the tenor trombones.

In 1921, Ernst Dehmel, a Berlin trombonist, patented a new design of contrabass trombone that added two independent rotary valves to the old bass trombone in F, still found in Prussian military bands of the time. The valves provide a fully chromatic range by supplying missing low register notes between the pedal F₁ in first position and the second partial C₂ in sixth (slide fully extended, without using a handle). The valves also provide alternatives for other notes in long slide positions, thus neither a longer slide with a handle nor a cumbersome double slide are needed. Dehmel's bass-contrabass instrument was the prototype for the modern F contrabass trombone designs that followed. In 1959, German organologist Hans Kunitz took Dehmel's instrument and filed a patent for a design with improved paddles allowing the use of the middle or fourth finger to engage the second valve. These instruments were first built as Cimbasso-Bassposaune in the 1960s by Gebr. Alexander in Germany, and subsequently by other German and Bohemian makers.