[8] Sen was about ten years old when he walked into Vimal Kumar's office at the Karnataka Badminton Association in Bengaluru, stood on his toes to reach the table and gave him a handwritten note with scoreline details.

Sen started off at Syed Modi International where he lost in pre-quarters to compatriot Sourabh Verma 14–21, 16–21.

[12] At the Junior Asian Championship, Sen was seeded as No.1 but lost in the pre-quarters to Lin Chun-yi 21–13, 23–25 and 20–22.

Sen defeated Cheam June Wei, a much higher ranked player than him 21–11, 21–16 in straight games at the New Zealand Open but lost to 2 time Olympic gold medallist and seed No.1 Lin Dan 21–15, 15–21 and 12–21.

He settled for the silver medal in the boys' singles after losing to Chinese player Li Shifeng in straight games 15–21, 19–21.

[16] Sen clinched the bronze medal at the BWF Junior World Championships after losing to the eventual champion Kunlavut Vitidsarn in the semi-finals 22–20, 16–21, 13–21.

He reached the 2nd round of 2020 All England Open, his 1st ever BWF Super 1000 Tournament before losing to champion and world No.1 Viktor Axelsen 17–21 and 18–21.

In December, he reached the semifinal of the World Championships where he lost to compatriot Srikanth Kidambi in a hard-fought match 21–17, 14–21, 17–21 and settled for a bronze medal.

[22] In January, he defeated the reigning world champion Loh Kean Yew in the India Open final, thus clinching his first Super 500 title.

[23] In the German Open, Lakshya defeated World No.1 Viktor Axelsen in the semifinals, but lost the finals to Kunlavut Vitidsarn.

[25][26] He subsequently withdrew from the Swiss Open, as he was tired after playing 2 back-to-back BWF tournaments finals.

After winning against his compatriot Prannoy H. S. in the round of 16, he defeated Chou Tien-chen in the quarter finals.

[32][33] He finished fourth after losing the bronze medal match to Lee Zii Jia, scripting the best ever performance by a male badminton player from India.

[34] Post his journey at the Olympics, Sen won the S300 title of Syed Modi International by defeating Singaporean Jason Teh 21-6, 21-7 in a dominating match.

[35] He ended the year by winning the bronze medal at the inaugural Kings Cup hosted by Lin Dan.

[40] In addition to his training sessions, Sen takes on ice baths, steam and sauna, and joint mobilisation work routines.