  We report here the discovery of a hot Jupiter at an orbital period of
$3.208666\pm0.000016$ days around TOI-1789 (TYC 1962-00303-1, $TESS_{mag}$ =
9.1) based on the TESS photometry, ground-based photometry, and high-precision
radial velocity observations. The high-precision radial velocity observations
were obtained from the high-resolution spectrographs, PARAS at Physical
Research Laboratory (PRL), India, and TCES at Th\"uringer Landessternwarte
Tautenburg (TLS), Germany, and the ground-based transit observations were
obtained using the 0.43~m telescope at PRL with the Bessel-$R$ filter. The host
star is a slightly evolved ($\log{g_*}$ = $3.939^{+0.024}_{-0.046}$), late
F-type ($T_{eff}$ = $5984^{+55}_{-57}$ K), metal-rich star ([Fe/H] =
$0.370^{+0.073}_{-0.089}$ dex) with a radius of {\ensuremath{$R_{*}$}} =
$2.172^{+0.037}_{-0.035}$ \(R_\odot\) located at a distance of
$223.56^{+0.91}_{-0.90}$ pc. The simultaneous fitting of the multiple light
curves and the radial velocity data of TOI-1789 reveals that TOI-1789b has a
mass of $M_{P}$ = $0.70\pm0.16 $ $M_{J}$, a radius of $R_{P}$ =
$1.40^{+0.22}_{-0.13}$ $R_{J}$, and a bulk density of $\rho_P$ =
$0.31^{+0.15}_{-0.13}$ g cm$^{-3}$ with an orbital separation of a =
$0.04873^{+0.00065}_{-0.0016}$ AU. This puts TOI-1789b in the category of
inflated hot Jupiters. It is one of the few nearby evolved stars with a
close-in planet. The detection of such systems will contribute to our
understanding of mechanisms responsible for inflation in hot Jupiters and also
provide an opportunity to understand the evolution of planets around stars
leaving the main sequence branch.
