On 17 November 2015, Nishu Kumar was signed by Bengaluru along with two fellow AIFF Elite Academy cadets, Daniel Lalhlimpuia and Malsawmzuala, in two years deal with an option to extend for one more year.[8] He represented the club at 2015–16 Bangalore Super Division.[9] Nishu made his debut for the club in 2016 AFC Cup against Ayeyawady United on 13 April 2016, which Bengaluru FC won 5–3.[10] He made his league debut against Mohun Bagan in the final game of the 2015-16 season on 23 April 2016, which Bengaluru lost the game for 5–0. Bengaluru was crowned the league champions of the seas, which helped Nishu securing his first trophy in his career.[11] Nishu was kept for the 2016-17 I-League season.[12] He played his first match of the season on 18 January 2017 in a 3–0 victory over Mumbai FC.[13] Nishu played his first continental match of the season as a substitute in the 2017 AFC Cup match on 4 April in Bengaluru's 0–1 victory over Maziya S&RC.[14] He scored his debut goal for the club in the 2017 AFC Cup match against Abahani Limited Dhaka on 18 April, which they ended up winning 2–0.[15] He played his last league match of the season on 22 April against DSK Shivajians, which ended with a massive score of 7–0 for Bengaluru.[16] In the following year, Bengaluru moved to Indian Super League from I-League as one of the two new entries.[17] Nishu was kept in the squad to compete in the 2017-18 Indian Super League season.[18] Nishu played his first match of the season and in ISL overall against Delhi Dynamos[broken anchor] (present Odisha FC) as a substitute on 26 November 2017, which ended in a 4–1 victory for Bengaluru.[19] He played his first continental match of the season in the 2018 AFC Cup match against Transport United on 23 January 2018, which ended in a 0–0 draw. Bengaluru had a good start in their first ISL season, as they qualified for the finals of the 2017-18 Indian Super League season after defeating FC Pune City on an aggregate score of 3–1 from both legs.[20] Nishu started as a substitute[21] in the final match against Chennaiyin FC on 17 March 2018, but they lost the final 2–3.[22] In May 2018, Nishu signed a two-year contract with Bengaluru till 2020.[23] He played his first match of the 2018-2019 Indian Super League season on 30 September 2018 in a 1–0 victory over Chennaiyin.[24] Nishu scored his first league goal in his career in the next match day on 7 October against Jamshedpur, which ended in a 2–2 draw.[25] Bengaluru had a standout campaign, as they were qualified for the finals once again in the 2018–2019 season after defeating NorthEast United in an aggregate score of 4–2 from both legs.[26] Nishu started in final against FC Goa[27] on 17 March 2018, which they ended up being victorious by a score of 1–0, thereby Nishu clinching his first Indian Super League title and winning the emerging player of the match award in the final eve.[28] After winning the title, Nishu played his first match of 2019-20 Indian Super League season against NorthEast United on 21 October 2019, which ended 0–0 to both sides.[29] He scored his first goal of the season in a 1–0 victory over Hyderabad on 30 January 2020.[30] Bengaluru continued their quest in the league, as they qualified for the knockout stage for the third consecutive time, but was defeated by ATK in an aggregate score of 3–2 from both legs.[31] In 2020 there were reports that Nishu Kumar will be leaving the club at the end of 2019–20 season.[32][33] He rejected a contract extension from the club and finally decided to leave the club. Throughout his time at Bengaluru FC, Nishu made 55 league appearances and scored two goals and played a pivotal role in the success of the club over the years.[34]
Kerala Blasters : 2020-Present
On 12 September 2020, it was officially confirmed that Nishu has finalised his move to Kerala Blasters FC, the southern rivals of his previous club.[35] The four-year deal with the Blasters made Nishu Kumar the highest-paid Indian defender surpassing the record of Sandesh Jhingan.[36] He made his Blasters debut on 26 November against NorthEast United FC, which ended in a 2–2 draw.[37] In February 2021, Nishu suffered a long-term knee injury which kept him out of action for the remaining games of the season. He was also not included in club's squad for the Durand Cup, that took place in September 2021.[38] After a period of six months, Nishu joined the Blaster's squad in the first week of October to complete the final leg of his rehabilitation.[39] He came back to action after seven months by playing in a pre-season friendly against Odisha FC in November ahead of the 2021-22 ISL season.[40] Nishu made his return in Indian Super League in Blasters' 0–0 draw over NorthEast United on 25 November 2021 by coming in as a substitute for Sahal Abdul Samad in the 73rd minute.[41][42] He scored his debut goal for the club against Odisha on 12 January 2022, where he netted a curler into the top-right corner, in a match which they won 0–2 at full-time.[43] After two seasons filled with injuries, Nishu made his first appearance of the season against ATK Mohun Bagan FC on 16 October 2022 as a substitute for Harmanjot Khabra in the 65th minute but the Blasters lost the match by a hefty score of 2–5.[44] After the ISL season, he was included in the Blasters squad for the 2023 Indian Super Cup,[45] and scored his first goal of the season against RoundGlass Punjab FC in the group-stage match on 8 April, where he scored the second goal for the Blasters as they won the match 3–1 at full-time.[46]