We present the discovery of a highly irradiated and moderately inflated ultra-hot Jupiter, TOI-1431b/MASCARA-5b (HD 201033b), first detected by NASAs Transiting Exoplanet Survey Satellite mission (TESS) and the Multi-site All-Sky CAmeRA (MASCARA). The signal was established to be of planetary origin through radial velocity measurements obtained using SONG, SOPHIE, FIES, NRES, and EXPRES, which show a reflex motion of $K=294.1pm1.1$ m s$^{-1}$. A joint analysis of TESS, MuSCAT2, and LCOGT photometry, radial velocity measurements, and the spectral energy distribution of the host star reveals that TOI-1431b has a mass of $M_{p}=3.14_{-0.18}^{+0.19}$ $rm{M_J}$ ($1000pm60$ M$_{oplus}$), an inflated radius of $R_{p}=1.51pm0.06$ $rm{R_J}$ ($16.9_{-0.6}^{+0.7}$ R$_{oplus}$), and an orbital period of $P=2.65022pm0.00001$ d. The planet orbits a bright ($mathrm{V}=8.049$ mag) and young ($0.29^{+0.32}_{-0.19}$ Gyr) Am type star with $T_{rm eff}=7690^{+400}_{-250}$ $rm{K}$, resulting in a highly irradiated planet with an incident flux of $langle F rangle=7.24^{+0.68}_{-0.64}times$10$^9$ erg s$^{-1}$ cm$^{-2}$ ($5300^{+500}_{-470}mathrm{S_{oplus}}$) and an equilibrium temperature of $T_{eq}=2370pm100$ K. TESS photometry also reveals a secondary eclipse with a depth of $124pm5$ppm as well as the full phase curve of the planets thermal emission in the red-optical. This has allowed us to measure the dayside and nightside temperature of its atmosphere as $T_mathrm{day}=2983^{+63}_{-68}$ K and $T_mathrm{night}=2556^{+62}_{-65}$ K, the second hottest measured nightside temperature. The planets low day/night temperature contrast ($sim$400 K) suggests very efficient heat transport between the dayside and nightside hemispheres.
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