Born in Burnaby, British Columbia, to Bill and Sandra Sinclair on June 12, 1983, Sinclair began playing soccer at the age of four for an under-7 team. Her father Bill Sinclair (1972) and uncles Brian (1972) and Bruce Gant (1990) were all Canadian amateur soccer champions while Brian and Bruce also played at the professional level. Her father Bill played for the University of British Columbia and the New Westminster Blues in the Pacific Coast Soccer League.

In 2001, Sinclair arrived at the University of Portland where she made an immediate impact on an already formidable soccer program. She recorded 23 goals and eight assists in her first season, leading all first-year students in NCAA Division I total scoring. She was named Freshman of the Year by Soccer America, and was a consensus All-America selection.

During her second season with the Pilots in 2002, Sinclair led Division I in goals with 26. She scored two goals during the national championship game against conference rival Santa Clara, the second of which was a golden goal that won the Pilots the national championship. Sinclair earned three different national Player of the Year honours, and was a finalist for the Hermann Trophy. Named West Coast Conference Player of the Year, she earned All-American honours for the second consecutive year. In the wake of her success for the Canadian national teams and American collegiate soccer, she was named by The Globe and Mail as one of the 25 most influential people in Canadian sports the same year.

Sinclair has won four professional championships with three teams: the 2010 WPS Championship with FC Gold Pride, the 2011 WPS Championship with Western New York Flash, and the 2013 and 2017 NWSL Championships with Portland Thorns FC. She won the national collegiate championships twice with the University of Portland Pilots: in 2002 and 2005. She was named WPS Player of the Week three times: once in 2010 and twice in 2011. In 2011, she was named MVP of the WPS Championship Final. With the Canadian national team, she has won the 2010 CONCACAF Women’s Gold Cup, a gold medal at the 2011 Pan American Games, a bronze medal at the 2012 Olympic Games, and a bronze medal at the 2016 Olympic Games. In 2002, she won silver with the Canadian team at the 2002 FIFA U-19 Women’s World Championship.

Sinclair was the leading scorer at the 2012 Summer Olympics. In 2002, she was awarded the Golden Boot for most goals scored and the Golden Ball as the best player at the FIFA U-19 Women’s World Championship. She was named Canadian Player of the Year 14 times: in 2000, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2016, and 2018, and nominated for FIFA World Player of the Year seven times in 2005, 2006, 2007, 2008, 2010, 2012, and 2016.

At the 2003 FIFA Women’s World Cup, Sinclair scored three goals for Canada on their way to a surprising fourth-place finish, their best in that competition to date. During the team’s first group stage match against Germany, she scored the first goal of the match in the fourth minute. Germany scored four goals to defeat Canada 4–1. After defeating Argentina 3–0, the team faced Japan in their last group stage match of the tournament. With goals from Sinclair and teammates Christine Latham and Kara Lang, Canada won 3–1 and placed second in their group to advance to the knockout stage. Canada faced China in the quarterfinal match on October 2 in Portland, Oregon and won 1–0 with the lone goal scored by Charmaine Hooper in the seventh minute. Having remained winless in all previous World Cup tournaments, Canada’s advancement to the semi-final was a historic change for the team. Canada was defeated by Sweden in the semi-final match 2–1 and faced the United States in the third-place match where they were defeated 3–1 and finished fourth at the tournament. Sinclair scored Canada’s goal in the 38th minute.

Sinclair chose to redshirt the 2003 season to play for Canada at the 2003 FIFA Women’s World Cup. She returned to Portland in 2004 and scored 22 goals for the Pilots. Following the season, she was named West Coast Conference (WCC) Player of the Year, received All-American honours, and was awarded the Hermann Trophy.

Sinclair made her 100th appearance on August 30, 2007, in a 0–0 friendly against Japan. On November 8, 2010, Sinclair scored the game-winning goal against Mexico in the final of the 2010 CONCACAF Women’s Gold Cup.

Sinclair was selected by FC Gold Pride eighth overall in the 2008 WPS International Draft for the inaugural season of top-tier American league Women’s Professional Soccer (WPS). Despite her team-leading six goals, FC Gold Pride finished last in the regular season standings during the 2009 season.

As the regular season champion, FC Gold Pride earned a direct route to the championship playoff game where they faced the Philadelphia Independence. Sinclair contributed two goals to FC Gold Pride’s 4–0 win to clinch the WPS Championship. Despite their successful season, the club ceased operations on November 16, 2010, due to not meeting the league’s financial reserve requirement.

On December 10, 2010, Western New York Flash announced that they had agreed to terms with the Canadian striker for the 2011 season. Sinclair helped guide the team to the regular season championship, leading the club with ten goals and eight assists. On August 27, 2011, Sinclair was named MVP of the 2011 WPS Championship Final after the Flash won the championship in Rochester, New York. Sinclair’s goal in the 64th minute gave the Flash a 1–0 lead over Philadelphia. When the game was forced to penalty kicks, Sinclair stepped up and completed the second one as the Flash players converted all five of their attempts.

At the 2012 Summer Olympics, Sinclair broke the record of most goals scored in the Olympics for women’s soccer, claiming the golden boot of the competition from two goals against South Africa, one against Great Britain, and three against the United States. She scored a hat-trick in a 4–3 extra time loss in the semi-final match against the American squad. Canada was unhappy with the performance of referee Christina Pedersen, who made a series of controversial decisions in favour of the Americans. Sinclair was ultimately fined a reported $3,500 and banned four matches for post match comments, which accused Pedersen of bias and deciding the result of the match before it had kicked off.

Sinclair subsequently finished the tournament as top scorer with six goals and led the Canadian women’s national soccer team to a bronze medal with a 1–0 win against France on August 9, 2012. Her remarkable effort as team captain and her performance in the semi-final earned her the honour of Canada’s flag bearer in the closing ceremony, as well as the Queen Elizabeth II Diamond Jubilee Medal.

In 2012, Sinclair was awarded the Lou Marsh Award and Bobbie Rosenfeld Award. The same year, she received the Diamond Jubilee Medal and was named Athlete of the Year by Sportsnet. In 2013, she was inducted into Canada’s Walk of Fame and received an honorary degree from Simon Fraser University.

Sinclair was the focus of a digital short documentary entitled The Captain in 2012. She was featured in an episode of The Difference Makers with Rick Hansen the same year. In May 2015, she was featured in the TSN documentary, RISE, along with the rest of the Canadian national team. She starred in a national television commercial for Coca-Cola during the summer of 2015.

On January 11, 2013, it was announced that Sinclair would play for the Portland Thorns FC for the inaugural season of the National Women’s Soccer League via the NWSL Player Allocation. Playing as team captain, she appeared in 20 games in the 2013 season and tied with Alex Morgan as the top scorer on the team with eight goals. Sinclair was named the league’s Player of the Month for the month of April after scoring two goals and serving one assist to help the team secure a 2–0–1 record.

Sinclair made her 200th appearance on December 12, 2013, scoring her 147th international goal in a 2–0 win over Scotland at the 2013 Torneio Internacional Cidade de São Paulo.

At the 2015 FIFA Women’s World Cup hosted by Canada, Sinclair scored the team’s only goal of the first group stage match against China, a 1–0 win, during a penalty kick awarded in the second minute of second-half stoppage time. Sinclair scored in the 42nd minute in a losing effort against England in the quarter-final. Canada lost the match 2–1.

In 2015, Sinclair, along with teammate Kadeisha Buchanan, was featured on a Canadian postage stamp commemorating the 2015 Women’s World Cup hosted by Canada. On June 30, 2017, she was appointed an Officer of the Order of Canada, the second-highest award a civilian can receive, with investiture of the award on January 24, 2018. Of the honour she said, “I am a very, very proud Canadian, I am proud of where I am from, and to be recognized in this nature is surreal. It’s not something you can dream about happening to you. I can dream of winning a World Cup or an Olympic gold medal, and that’s my job, but to have your country recognize you – I don’t even know what to say.”

In the 2017 season, she led the Thorns in scoring with eight goals during the regular season, with the team finishing second. In the playoffs, she scored a goal, tying the record for NWSL playoff goals, en route to the team’s second championship in the NWSL Final. In the pandemic-shortened 2020 season, Sinclair led the Thorns with six goals, five more than any of her teammates, helping the Thorns win the NWSL Fall Series.

Sinclair was featured on the Canadian version of EA Sports’ FIFA 16 (2016) video game. Along with Portland Thorns FC teammates Alex Morgan and Steph Catley, Sinclair was one of the first women to appear on the cover of any EA Sports game. In July 2017, Sinclair partnered with A&W and the Multiple Sclerosis Society of Canada on a nationwide awareness campaign for multiple sclerosis.

At the 2019 FIFA Women’s World Cup hosted by France, Sinclair scored one goal against the Netherlands, which is her tenth goal in five different World Cup editions, an achievement only accomplished by Brazilian Marta. However, Canada went out in the round of 16, after losing 0–1 against Sweden.

In December 2019, she was named the Canada Soccer’s Player of the Decade by the Canadian Soccer Association.