Context. M 17 is one of the best studied giant HII regions in our galactic neighborhood. It should also provide a suitable environment for the class of fully ionized jets externally irradiated by the presence of nearby hot stars. However, no such jets have been observed thus far in M 17. Aims. We report on a visible imaging survey of the M 17 nebula with the goal of identifying likely shock-excited nebulosities. Methods. We imaged M 17 through narrow-band filters centered on the most intense visible lines of [OIII], H +[NII], [SII], and H . We obtained follow-up spectroscopy of the only jet-like structure identified in the images. We also used published X-ray observations of M 17 obtained with the Chandra X-ray Observatory, as well as infrared data obtained with the Very Large Telescope and with the Spitzer Space Telescope, to look for evidence of a jet-driving source. Results. We have detected what appears to be the first jet identified in M 17 visible HII region. The jet is composed of a set of knots, two of which have significant radial velocities with respect to the HII region, and a distant arc-like bright nebulosity that may represent an early episode of intense mass loss by the jet-driving source. The follow-up spectra of the structures composing the jet, including the arc, support this interpretation by revealing intense forbidden lines of [NII] and [SII] due to enhanced collisional excitation in shocks. The presence of a X-ray source, most likely a young stellar object, at a position where the jet launching source should be expected to lie reinforces the interpretation. We identify a tentative near-infrared counterpart of the X-ray source, although it is o set by 1: 00 9 from the nominal position of the X-ray source, which is almost three times the radius of its positional uncertainty. The very weak [OI] emission in the spectra of the jet knots and the arc suggests that they are nearly fully ionized, in agreement with the environment in which the jet is propagating.