In the Babylonian star catalogues, Triangulum, together with Gamma Andromedae, formed the constellation known as MULAPIN (𒀯𒀳) "The Plough".

It is notable as the first constellation presented on (and giving its name to) a pair of tablets containing canonical star lists that were compiled around 1000 BC, the MUL.APIN.

The Plough was the first constellation of the "Way of Enlil"—that is, the northernmost quarter of the Sun's path, which corresponds to the 45 days on either side of summer solstice.

Its first appearance in the pre-dawn sky (heliacal rising) in February marked the time to begin spring ploughing in Mesopotamia.

[3] Eratosthenes linked it with the Nile Delta, while the Roman writer Hyginus associated it with the triangular island of Sicily, formerly known as Trinacria due to its shape.

[4] It was also called Sicilia, because the Romans believed Ceres, patron goddess of Sicily, begged Jupiter to place the island in the heavens.

[4][6] Later, the 17th-century German celestial cartographer Johann Bayer called the constellation Triplicitas and Orbis terrarum tripertitus, for the three regions Europe, Asia, and Africa.

The brightest member is the white giant star Beta Trianguli of apparent magnitude 3.00,[5] lying 127 light-years distant from Earth.

[12] It is actually a spectroscopic binary system; the primary is a white star of spectral type A5IV with 3.5 times the mass of the Sun that is beginning to expand and evolve off the main sequence.

[14] Making up the triangle is Gamma Trianguli, a white main sequence star of spectral type A1Vnn of apparent magnitude 4.00 about 112 light-years from Earth.

Delta is a spectroscopic binary system composed of two yellow main sequence stars of similar dimensions to the Sun that lies 35 light-years from Earth.

HD 9446 is a Sun-like star around 171 light-years distant that has two planets of masses 0.7 and 1.8 times that of Jupiter, with orbital periods of 30 and 193 days respectively.

[28] A distant member of the Local Group, it is about 2.3 million light-years away, and at magnitude 5.8 it is bright enough to be seen by the naked eye under dark skies.

Being a diffuse object, it is challenging to see under light-polluted skies, even with a small telescope or binoculars, and low power is required to view it.

[34] These two plus another four nearby dwarf irregular galaxies constitute the NGC 672 group, and all six appear to have had a burst of star formation in the last ten million years.

Together with two isolated dwarf galaxies, these fourteen appear to be moving in a common direction and constitute a group possibly located on a dark matter filament.