Giant radio galaxies ( GRGs ) are one of the largest astrophysical sources in the Universe with an overall projected linear size of \sim 0.7 Mpc or more .
Last six decades of radio astronomy research has led to the detection of thousands of radio galaxies .
But only \sim 300 of them can be classified as GRGs .
The reasons behind their large size and rarity are unknown .
We carried out a systematic search for these radio giants and found a large sample of GRGs .
In this paper , we report the discovery of 25 GRGs from NVSS , in the redshift range ( z ) \sim 0.07 to 0.67 .
Their physical sizes range from \sim 0.8 Mpc to \sim 4 Mpc .
Eight of these GRGs have sizes \geq 2 Mpc which is a rarity .
Here , for the first time , we investigate the mid-IR properties of the optical hosts of the GRGs and classify them securely into various AGN types using the WISE mid-IR colours .
Using radio and IR data , four of the hosts of GRGs were observed to be radio loud quasars that extend up to 2 Mpc in radio size .
These GRGs missed detection in earlier searches possibly because of their highly diffuse nature , low surface brightness and lack of optical data .
The new GRGs are a significant addition to the existing sample that will contribute to better understanding of the physical properties of radio giants .