[3] In 2011, he was selected for AIFF Elite Academy[4] as a part of Tata Tea & Inter Milan Soccer Stars talent hunt.

[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.

[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.

[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.

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] 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.

[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.

[48] In June 2017, Nishu was called up for the senior national team to compete in the 2019 AFC Asian Cup Qualifiers camp for a game against Kyrgyzstan.