Bronze began playing for Sunderland at under-12 academy level and joined the senior team when she turned 16 in 2007. She previously captained the under-16 team. In 2007–08, Bronze was named Manager’s Player of the Year as Sunderland finished third in the FA Women’s Premier League Northern Division. The next season she helped them win the Northern Division and gain promotion to the National Division. Bronze also appeared in the 2009 FA Women’s Cup final, claiming the Player of the Match award in Sunderland’s 2–1 defeat to Arsenal.

Bronze was called into the England under-17 squad in March 2007, while she was playing for Blyth Town WFC in the Northern Girls Tyne Tees League. She went on to participate in the England under-17 squad that came fourth in the FIFA U-17 Women’s World Cup in New Zealand. Bronze was also part of the England under-19 squad that won the UEFA Women’s Under-19 Championship in Belarus during July 2009 and part of the squad the following year that finished runners-up to France in the finals held in June 2010 in Macedonia.

That summer, Bronze moved to the United States to study at the University of North Carolina at Chapel Hill and play for the North Carolina Tar Heels women’s soccer team, the winningest Division 1 team in the country. She won a scholarship from coach Anson Dorrance after impressing him during several soccer camps. Bronze featured prominently in the midfield for the team, eventually becoming the first British player to win an NCAA Cup in December 2009. All-American honours followed for Bronze, who scored three goals in 24 games. She then returned to Sunderland in the Premier League National Division.

In September 2010 it was revealed that Bronze had signed for Everton, when she was named in their UEFA Women’s Champions League squad. She debuted for Everton against MTK in Hungary, but continued to play for Sunderland while her new club awaited the 2011 FA WSL.

She was called into an England under-20 training camp in January 2010. After featuring in all three games during the 2010 FIFA U-20 Women’s World Cup, Bronze made her debut for the England under-23 team in a 2–1 win over Germany in September 2010.

In November 2012, Bronze left Everton to sign for local rivals Liverpool, following Natasha Dowie and Fara Williams who had made the same move days earlier.

Bronze was part of the Liverpool side that won the FA WSL in 2013 and again in 2014. The following year, she was awarded the PFA Women’s Players’ Player of the Year. Following her second league title, she departed Liverpool to sign for Manchester City.

Bronze made her debut for the England senior team on 26 June 2013 as a substitute in the 67th minute for Dunia Susi in a friendly against world champions Japan at the Pirelli Stadium in Burton-upon-Trent. She had a claimed goal disallowed in the 89th minute of the 1–1 draw. The following month, she was an unused member of the squad at Euro 2013 in Sweden, a group stage exit.

Bronze scored her first England goal on 14 June 2014, in a 3–0 away win over Belarus in World Cup qualification. She scored again on 17 September, as England concluded their qualification process with a 10–0 away win over Montenegro and a 100% record. On 23 November Bronze started England’s 0–3 defeat by Germany in the first England women’s match at Wembley Stadium.

Bronze was part of the England squad at the 2015 Women’s World Cup. In the last 16 against Norway in Ottawa, she scored the winning goal from outside the penalty area as England came from behind to win 2–1, their first knock-out win at the World Cup. She also went on to score what proved to be the quarter-final winner against Canada in Vancouver as she netted England’s second from a header in the 14th minute. She was widely praised as one of the best performers for England team at the World Cup. For her performances in the tournament, Bronze was included in the 2015 FIFA Women’s World Cup All Star Team and shortlisted for the Golden Ball – the award given to the best player at the Women’s World Cup.

In her first year at Manchester City, Bronze scored two goals from the full-back position, helping City to second place in the league, meaning they qualified for the UEFA Women’s Champions League for the first time. In 2016, her second season in Manchester, she scored two league goals as the Blues went unbeaten for the entire season. The defender contributed to an outstanding record which saw Manchester City only concede four league goals. She also helped Manchester City to their second FA WSL Cup win in three years, scoring the winning goal in the 105th minute of the final. Bronze was also named FA WSL 1 Players’ Player of the Year. She played a part in both the home and away leg of Manchester City’s first ever Champions League games, scoring two and assisting two in a 6–0 aggregate win over Russian champions Zvezda Perm. She ended competition with eight appearances, as Manchester City reached the semi-finals of the 2016–17 edition of the UEFA Women’s Champions League, with their title hopes ended in late April when they lost Olympique Lyonnais a 3–2 on aggregate. On 23 April 2017, Bronze was named PFA Women’s Players’ Player of the Year for second time; selected in the PFA WSL Team of the Year and Women’s Champions League Squad of the Season. Later that year, she was shortlisted for the UEFA Women’s Player of the Year Award and The Best FIFA Women’s Player Award, but finished eighth and ninth respectively in the voting.

In August 2017, Bronze signed a three-year contract with Olympique Lyonnais. In the 2017–18 season of the UEFA Women’s Champions League, Bronze made eight appearances, scoring two goals as Lyon reached the final. Lucy featured in the final match of the UEFA Women’s Champions League and helped Lyon win the competition. In the Division 1 Féminine league, Lucy made nineteen appearances, scoring two goals, as Lyon captured its twelfth straight league title. Bronze was named in the Team of the Year for D1 Feminine and Women’s Champions League Squad of the Season. In the Coupe de France, Bronze and Lyon were unable to defend their Coupe de France title, losing to Paris Saint-German in the final. Bronze has been shortlisted for the inaugural Women’s Ballon d’Or award, was one of 10 players nominated for UEFA Women’s Player of the Year Award and The Best FIFA Women’s Player Award, but finished sixth, fifth and sixth respectively.

In July 2017, she was named in the squad for the UEFA Women’s Euro 2017, which England lost 3–0 to eventual winners Netherlands in the semi-final. For her performances in the tournament, Bronze was included in the 2017 UEFA Team of the Tournament.

Bronze captained England for the first time in the 2018 SheBelieves Cup opening match against France.

During the 2018–19 season, Bronze made 29 appearances for the Lyon in all competitions, scored two goals and collected her second Division 1 Féminine league title winner’s medal; she also won Coupe de France Féminine title and helped Lyon win a second consecutive UEFA Women’s Champions League trophy. In 2019, for her performances in the tournaments, the defender finished as runner-up for the women’s Ballon d’Or award, was named UEFA Women’s Player of the Year Award and finished third in the voting for The Best FIFA Women’s Player Award.

Bronze helped Lyon win Trophée des Championnes in 2019 – a first historic new trophy against PSG. At the end of the season, Bronze confirmed that she would be leaving Lyon, following the expiration of her contract. She won nine trophies in three seasons with the club.

In 2019, Bronze was part of the England team that won the SheBelieves Cup in the United States. Later that year, Bronze was selected in England’s World Cup squad. As part of England’s social-media facing squad announcement, her name was announced by former footballer Alex Scott. Bronze scored during a 3–0 victory over Norway in the quarter-finals of the 2019 FIFA Women’s World Cup. England finished the tournament in fourth place. Bronze ended up winning the tournament’s silver ball, being the second best player in the tournament. After the World Cup, Bronze played in an unfamiliar central midfield role in friendlies against Belgium and Norway, having previously played there in the 2019 SheBelieves Cup, with England manager Phil Neville likening her to Philipp Lahm. Neville said: “We have a two-year period now where playing Lucy in midfield might be one of the risks we take … Pep Guardiola did it with Philip Lahm. He was voted one of the best right-backs, but he put him into midfield.”

On 8 September 2020 Bronze rejoined Manchester City on a two-year deal, following the conclusion of her contract with Olympique Lyonnais, which brought the curtain down on a trophy-laden three-year spell in France.