He defeated his friend Amit Paul on the basis of audience votes - totalling a whopping 70 million SMSs.
Bollywood star John Abraham and lyricist Javed Akhtar gave away the prizes after the pulse-racing grand finale of Sony TV's show "Indian Idol" at the Exhibition Ground in Okhla.
"Either I win or Amit wins, I am happy with either result. Amit has been my friend since the beginning of the show and the competition part came only when we were the only two people left," Prashant said before the results were announced.
Clad in an embroidered blue kurta and white churidar, Amit sang a number of lilting Hindi film songs and won over the audience as the panel of judges including Abraham, Akhtar, music composer Anu Malik, singers Alisha Chenoy and Udit Nayaran clapped.
Among the audience here were the families of both participants, sometimes praying nervously, sometimes breaking into wide smiles.
Prashant, a 24-year-old Kolkata Police constable of Nepali origin, hails from Darjeeling while runner-up Amit, 24, is from Shillong.
In the third season of Sony TV's music competition, the battle for the top honour was between the two contestants from northeast - and the hilly region was in rapture in recent days as people of all ages queued up to send their votes by SMSs.
Though Amit was not behind in charming audiences around the globe, Prashant's youthful voice and ability to sing different genres of songs with his unique style won the viewers' hearts.
He was not only audiences' favourite, he earned praise from all judges too.
Before the grand finale, the two contestants met Prime Minister Manmohan Singh and Congress president Sonia Gandhi and sought their blessings.
Earlier, film personalities like Abraham, Bipasha Basu, Sanjay Dutt and Riteish Deshmukh kept visiting the show to boost the morale of the singers.
The season three of the Sony TV's talent hunt show has apparently been a huge success with more than 75 million viewers watching it.
Unfortunately, this time too no girl could reach the finals.
After the preliminary rounds, 13 contestants were short-listed for the gala round that included Emon Chatterjee (West Bengal), Ankita Mishra (Kanpur), Meiyang Chang (Jharkhand), Puja Chatterjee, Deepali Kishore (Bihar), Abhishek Kumar (Bangalore), Parleen Singh Gill (Haryana), Charu Semwal (Uttaranchal), Smita Adhikari (West Bengal), Jolly Das (West Bengal), Richa Aneja (Punjab).
In the first edition of the show, Abhijit Sawant had emerged the Indian Idol, while the second season went to Sandeep Acharya.