We report the discovery of two transiting planets orbiting K2-290 (EPIC 249624646), a bright (V=11.11) late F-type star residing in a triple-star system. It was observed during Campaign 15 of the K2 mission, and in order to confirm and characterise the system, follow-up spectroscopy and AO imaging were carried out using the FIES, HARPS, HARPS-N, and IRCS instruments. From AO imaging and Gaia data we identify two M-dwarf companions at a separation of $113 pm 2$ AU and $2467_{-155}^{+177}$ AU. From radial velocities, K2 photometry, and stellar characterisation of the host star, we find the inner planet to be a mini-Neptune with a radius of $3.06 pm 0.16 R_{oplus}$ and an orbital period of $P = 9.2$ days. The radius of the mini-Neptune suggests that the planet is located above the radius valley, and with an incident flux of $Fsim 400 F_{oplus}$, it lies safely outside the super-Earth desert. The outer warm Jupiter has a mass of $0.774pm 0.047 M_{rm J}$ and a radius of $1.006pm 0.050R_{rm J}$, and orbits the host star every 48.4 days on an orbit with an eccentricity $e<0.241$. Its mild eccentricity and mini-Neptune sibling suggest that the warm Jupiter originates from in situ formation or disk migration.
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