The second seed and favourite overcame a tough challenge from Thai Tanongsak Saensomboonsuk to win 21-19, 14-21, 21-17 in one hour and 12 minutes at the Babu Banarasi Das Indoor Stadium.
In the women's singles final, second seed P.V. Sindhu of India failed to come out victorious against Indonesian seventh seed Lindaweni Fanetri.
Kashyap, World No.20, came from behind to win the first game. Despite a sprain in his back which he has had throughout the tournament, Kashyap did not falter and came back from 7-13 down to first level at 17-all and then win the game.
In the second game, the Thai fought back and dictated terms, not giving the lead even once to Kashyap.
The third game was dominated by Kashyap who took the lead after being level at 6-all.
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The Thai made many simple errors at crucial junctures giving the lead to the Indian and Kashyap's exquisite smashes proved too good for the World No.41.
"This was the toughest match of the tournament. He was very good at the net," said the 26-year-old Kashyap, who improved his record against Tanongsak to 2-3.
"It was a tough tournament for me as I was playing with an abdominal injury and sprained my back in the quarterfinal but just glad to win this. At one point, I thought I wouldn't even play the tournament. The crowd support was also superb."
Earlier, World No.24 Sindhu lost 15-21, 21-18, 18-21 in a marathon match lasting one hour and 12 minutes. Fanetri levelled their head-to-head to one-all, after having lost in the qualification rounds of the All England Open this year.
The first game was completely dominated by the seventh seed. Fanetri was also aided by the unforced errors of Sindhu, who regularly out-hit her shots which landed outside the third court. Down 5-11, the Hyderabadi could never come back and lost the game.
Sindhu came back strongly in the second game taking a 12-5 lead. Deceiving net play and supreme reach gave the World No.33 the edge. The Indian excelled at the net in the penultimate game as she clinched 12 net points to Fanetri's five.
The Indonesian came back strongly to almost the level the game but with the crowd chanting her name, Sindhu clinched the last crucial points to take the match into the decider.
The decider was a thriller. From 10-all Fanetri took the initiative, not giving too many opportunities, going ahead 14-10.
The second seed fought back with some excellent cross court smashes and levelled at 16-all, going on to take the lead in the match for the final time (17-16). But Fanetri won the next five out of six points to clinch the game and match.
"Sindhu plays really well and considering she is only 17, she has lot of titles to win in the future," said the winner.
Final results:
Men's singles: 2-Parupalli Kashyap (IND) bt 14-Tanongsak Saensomboonsuk (THA) 21-19, 14-21, 21-17.
Women's singles: 7-Lindaweni Fanetri (INA) bt 2-P.V. Sindhu (IND) 21-15, 18-21, 21-18.
Men's doubles: 4-Sung Hyun Ko/Yong Dae Lee (KOR) bt Ji Wook Kang/Sang Joon Lee (KOR) 21-13, 21-19.
Women's doubles: 2-Savitree Amitrapai/Sapsiree Taerattanachai (THA) bt 3-Komala Dewi/Jenna Gozali (INA) 21-12, 21-6.