[14] He signed for Major League Soccer side Kansas City Wizards in 2010, becoming the third player from the subcontinent of note to go abroad.

His goal tally also ranks him fourth in the all-time list among international goal-scorers, behind Cristiano Ronaldo, Lionel Messi and Ali Daei.

[23] He represented the club in 2002 Durand Cup where although his team failed to qualify for quarterfinal stage, Chhetri made an appearance in four games and scored a goal.

The first came against Sporting Goa while the second came against Indian Bank as Mohun Bagan once again finished in the bottom half of the table, in ninth place.

[33] However, despite Chhetri's best efforts, Delhi were eliminated in the pre-quarter final round after losing 1–0 to Tamil Nadu in extra time.

[33] Then, during the 2006–07 season, Chhetri scored a total of twelve goals in the league for JCT as the club finished in second place, behind Dempo.

These clubs were Leeds United of the Football League One and Estoril Praia of the Liga de Honra, the second division of Portugal.

[46] Midway through the season though, reports came out suggesting that two Major League Soccer teams were interesting in Chhetri, along with his international teammate Steven Dias.

"[52] Then on 30 August 2009 it was announced by the Hindustan Times that Chhetri had signed a three-year contract with English Football League Championship side Queens Park Rangers but that he was denied a work permit by the British government.

"[53] Chhetri made his debut for Dempo against Air India on 14 September in a Durand Cup fixture, scoring a penalty in a 4–1 win.

[54] In March 2010 it was announced that Chhetri was on trial with the Kansas City Wizards of Major League Soccer and that he had played during their pre-season games.

[56] On 14 April 2010, Chhetri made his debut for the Wizards in a U.S. Open Cup qualification play-in game against the Colorado Rapids.

[59] On 25 July 2010, Chhetri made an appearance for the Wizards against Manchester United, coming on as a substitute for Teal Bunbury in the 69th minute as Kansas City won the match 2–1.

[70] On 13 February 2013, it was announced that in order to get more playing time Chhetri would be loaned out to Churchill Brothers in the I-League for the remainder of the season.

[71] He made his debut for Churchill Brothers on 21 February 2013 against Dempo in the first game of 2012–13 Goa Professional League season championship round in which Chhetri started and scored a brace in a 2-0 win.

[72] He made his continental debut on 26 February 2013 against Kitchee in the 2013 AFC Cup in which Chhetri started as Churchill Brothers lost 0–3.

[76] He made his debut for the club in their opening game on 22 September 2013 against Mohun Bagan in which he came on as a 46th-minute substitute for Beikhokhei Beingaichho as Bengaluru managed a 1–1 draw.

Sunil scored his first goal of the 2014–15 season in the 7th round away to Mohun Bagan from a Eugeneson Lyngdoh cross but couldn't prevent his team from going down 4–1.

Chhetri's second goal was a 30-yard strike, where he received the ball from C. K. Vineeth, beat one defender and unleashed a screamer to give Bengaluru the lead.

[102] On 12 June 2005 Sunil scored his first goal on his debut for the senior India national football team against Pakistan in the eventual 1–1 draw.

Chhetri was involved in the build-up to Pappachen Pradeep's decisive goal as India beat Syria 1–0 in the final to become the first champions of the tournament since 1997.

[119] His first goal was originally disallowed for offside by Uzbek referee Valentin Kovalenko, who changed his mind after consulting his assistant.

[123] He featured in the other three games in the round robin stage of the tournament, including the "dress rehearsal" for the final against Syria, but did not score.

[134] However, after this match, Chhetri was disappointed with the poor turnout at the stadium and he uploaded a video on Twitter requesting people to come to Mumbai Football Arena to support the Indian team.

His video went viral and garnered widespread support from fans, celebrities and legendary cricketers like Sachin Tendulkar and Virat Kohli.

[143] Due to some injuries after 2021–22 Indian Super League season, Sunil was not able to participate for International friendlies against Bahrain and Belarus which were held in March 2022.

Then he made his appearance against Jordan in an international friendly fixture which was played as a part of preparing for 2023 AFC Asian Cup Qualifiers which was going to be held in June 2022.

On 8 June 2022, Chhetri played against Cambodia in 2023 AFC Asian Cup Qualifiers where he scored a brace, from a penalty spot and a header from a cross from Brandon Fernandes, by which India won 2–0 in Salt Lake Stadium.

[152] On 16 May 2024, Chhetri announced that he would retire from international football after his last match against Kuwait on 6 June at the Salt Lake Stadium in Kolkata, which eventually ended in a 0–0 draw.

[167] On 27 September 2022, FIFA launched a documentary on FIFA+, of three episodes named 'Captain Fantastic', which documents his pre-teen anguish, his debut for India aged 20, his romance with his future wife and his early days and peak as a football player.