Sandeep Lamichhane was born on 2 August 2000 in Aruchaur, Syangja, Nepal. During his childhood, he considered Sachin Tendulkar and Shane Warne as his cricketing idols. Then he moved to Chitwan district and started training at Chitwan Cricket Academy which is run by former captain Raju Khadka. During a visit by the captain Paras Khadka and former coach of Nepal Pubudu Dasanayake, Sandeep was told to bowl in the nets and was selected for the national under-19 training camp.

He made his List A cricket debut in the 2015–17 ICC World Cricket League Championship on 16 April 2016 against Namibia. Prior to his List A debut, he was named in Nepal’s under-19 squad for the 2016 Under-19 Cricket World Cup. In their second match against Ireland under-19s he took a hat-trick, becoming the fifth bowler to take a hat-trick in under-19 world cup history. He was adjudged man of the match with figures of 5/27.

He finished the tournament as second highest wicket taker with 14 wickets at an average of 17.07 and strike rate of 21.9. In September 2016 Lamichhane received a letter from former Australian captain Michael Clarke, inviting him to play at the Sydney-based Western Suburbs District Cricket Club. In the 2017 ACC Under-19 Asia Cup, he took bowling figures of 5/8 which restricted Malaysia under-19s to a total of 45 and was named the man of the match.

In July 2018, Lamichhane released his first song Udash thiyo from the album Pratikshya-the waiting.

In January 2018, he was included in the list of players for auction in the 2018 Indian Premier League (IPL). He was bought by Delhi Daredevils and became the first Nepalese cricketer to get a contract in the IPL. Indian Prime minister Narendra Modi commented that the relationship between India and Nepal had been strengthened because of the signing.

In March 2018, he was drafted to play for the St Kitts and Nevis Patriots in the Caribbean Premier League.

In May 2018, he made his senior Twenty20 debut for the Delhi in the IPL, becoming the first Nepalese cricketer to play in the IPL. He took a wicket for 25 runs on his debut match against Royal Challengers Bangalore. In the tournament he took five wickets in three matches with a bowling average of 16.40.

In June 2018 Lamichane was selected to play for the Montreal Tigers in the inaugural edition of the Global T20 Canada tournament. In the tournament he took eight wickets in five matches at an average of 19.62. In September 2018, he was named in Nangarhar’s squad in the first edition of the Afghanistan Premier League tournament, going on to play in one match in the tournament.

In October 2018, he was signed by the Melbourne Stars for the Big Bash League (BBL), becoming the first cricketer from Nepal to play in the BBL. Later the same month, he was named in the squad for Sylhet Sixers, following the draft for the 2018–19 Bangladesh Premier League. In November 2018, Lamichhane was named in Lahore Qalandars’s squad in the fourth edition of the Pakistan Super League. In March 2019, he was named as one of eight players to watch by the International Cricket Council (ICC) ahead of the 2019 Indian Premier League tournament. The following month, Lamichhane said he recognised the huge learning curve of playing in the IPL and that it had “changed his life”.

In January 2018, he was named in Nepal’s squad for the 2018 ICC World Cricket League Division Two tournament. In their opening match against Namibia, he was adjudged man of the match with bowling figures of 4/18 in 8.2 overs. He also shared a crucial final wicket partnership of 18 runs with Basanta Regmi to win the match by one wicket. In the third match against the United Arab Emirates, he took 3/30 to help reduce the opponent to 114 runs. In the fourth match against Kenya, he took his first five wicket haul in List A cricket, with 5/20, and was again named the man of the match.

In February 2018, the International Cricket Council (ICC) named Lamichhane as one of the ten players to watch ahead of the 2018 Cricket World Cup Qualifier tournament. Following the conclusion of the tournament, the ICC went on to name Lamichhane as the rising star of Nepal’s squad.

In May 2018, he was added to the ICC Rest of the World XI team, for the Hurricane Relief T20 Challenge against the West Indies at Lord’s. He made his making his T20I debut in the match.

In July 2018, he was named in Nepal’s squad for their ODI series against the Netherlands. These were Nepal’s first ODI matches after gaining ODI status during the 2018 Cricket World Cup Qualifier. Ahead of the matches, the ICC named him as the key player for Nepal. He made his T20I debut for Nepal in July in the third match of the 2018 MCC Tri-Nation Series, against the Netherlands. He made his ODI debut for Nepal against the Netherlands on 1 August 2018.

In August 2018, he was named in Nepal’s squad for the 2018 Asia Cup Qualifier tournament. In October 2018, he was named in Nepal’s squad in the Eastern sub-region group for the 2018–19 ICC World Twenty20 Asia Qualifier tournament. He was the leading wicket-taker during the tournament, with 24 dismissals in six matches.

In June 2019, he was selected to play for the Toronto Nationals franchise team in the 2019 Global T20 Canada tournament. In July 2020, he was named in the Jamaica Tallawahs squad for the 2020 Caribbean Premier League.

In June 2019, he was named in Nepal’s squad for the Regional Finals of the 2018–19 ICC T20 World Cup Asia Qualifier tournament. He made his first-class debut on 6 November 2019, for Nepal against the Marylebone Cricket Club (MCC), during the MCC’s tour of Nepal. On 12 February 2020, in the match against the United States in the 2020 Nepal Tri-Nation Series, Lamichhane took his first five-wicket haul in an ODI match. On 29 February 2020, in the match against Malaysia in the Eastern Region group of the 2020 Asia Cup Qualifier, Lamichhane became the first bowler for Nepal to take 100 wickets in Twenty20 cricket. In September 2020, he was one of eighteen cricketers to be awarded with a central contract by the Cricket Association of Nepal.