The first detection of l-C₃H⁺ was reported, disputed, and confirmed in 2012-2014. In 2012 Pety et al. reported the observation of l-C₃H⁺ toward the Horsehead photon-dominated region using the IRAM 30 m telescope. Six lines in the survey were assigned to l-C₃H⁺. In 2013 the detection was disputed by Huang et al. on the basis of very accurate quantum chemical calculations of the rotational constants of l-C₃H⁺, suggesting that the line assigments were incorrect. But in 2014 Brünken et al. remeasured the rotational spectrum of l-C₃H⁺ and found that the orginal assignments of Pety et al. were correct. Subsequently, Guzmán et al. improved upon the spatial resolution of the initial detection in the Horsehead PDR.

While various neutral linear C_nH compounds have been identified in space, from the ethynyl radical through the n=8 compound, along with anions, l-C₃H⁺ is the first polyatomic linear C_nH⁺ cation to be detected in space.