We consider a one-dimensional classical Coulomb gas of N like-charges in a harmonic potential -also known as the one-dimensional one-component plasma (1dOCP). We compute analytically the probability distribution of the position xmax of the rightmost charge in the limit of large N . We show that the typical fluctuations of xmax around its mean are described by a non-trivial scaling function, with asymmetric tails. This distribution is different from the Tracy-Widom distribution of xmax for the Dyson's log-gas. We also compute the large deviation functions of xmax explicitly and show that the system exhibits a third-order phase transition, as in the log-gas. Our theoretical predictions are verified numerically.The Tracy-Widom (TW) distribution has emerged ubiquitously in diverse systems in the recent past [1, 2]. It was originally discovered as the limiting distribution of the top eigenvalue x max of an N × N Gaussian random matrix [3]. Since then, it has appeared in various areas of physics [4,5], mathematics [6,7], and information theory [8]. For example, in physics it has appeared in stochastic growth models and related directed polymer in 1 + 1 dimensional random media belonging to the Kardar-Parisi-Zhang (KPZ) universality class [9-15], non-intersecting Brownian motions [16], non-interacting fermions in a one-dimensional trapping potential [17][18][19], disordered mesoscopic systems [20] and even in the YangMills gauge theory in 2-dimensions [16]. It has also been measured experimentally in several systems including liquid crystals [21], coupled fiber lasers [22] or disordered superconductors [23]. The TW distribution describes the probability of typical fluctuations of x max around its mean. In contrast, the atypical fluctuations of x max to the left and right, far from its mean, are described respectively by the left and right large deviation tails. These tails have been computed explicitly [24][25][26][27] and shown to correspond to two different thermodynamic phases separated by a third order phase transition [28,29]. Similar third order phase transitions have also been found in a variety of other systems [29][30][31][32][33][34][35].For Gaussian ensembles in random matrix theory (RMT), the joint probability distribution function (PDF) of the N real eigenvalues {x 1 , · · · , x N } is known explicitly [36,37] P({x i }) = B N e