[3] Prannoy came to prominence after winning the silver medal in Boys' singles at the 2010 Summer Youth Olympics.

[11] Prannoy surprised one and all by reaching the final of the 2014 Vietnam Open Grand Prix where he lost to top seed and tournament favourite Dionysius Hayom Rumbaka of Indonesia.

Prannoy started off the year on a good note reaching the semifinals of the 2015 India Open Grand Prix Gold.

His greatest victory came in the pre-quarters of the 2015 India Super Series, when he beat an in-form world number 2 Jan Ø. Jørgensen in 3 sets.

Prannoy started 2016 on a good note by beating German ace Marc Zwiebler in the finals of the Swiss Open Grand Prix gold 21–18, 21–15.

[16] At the 2017 U.S. Open, he defeated Vietnamese Nguyễn Tiến Minh to reach the finals, where he beat compatriot Parupalli Kashyap to win the title.

[17] Prannoy participated in the 2018 Commonwealth Games, where he finished in fourth place after being beaten by Rajiv Ouseph of England in the bronze medal match.

However, he came back strongly in the second half of the year, most notably defeating reigning Olympic champion Viktor Axelsen in the 2nd round of the 2021 Indonesia Masters in November.

In the quarter-final against Malaysia, he won the decider match against Leong Jun Hao to assure India a semi-final spot and its first-ever medal in the Thomas Cup.