Mackenzie Arnold

Canberra United

In 2012, Arnold joined Canberra United from Perth Glory ahead of the 2012–13 W-League.

Western Sydney Wanderers FC

Arnold joined Western Sydney Wanderers in 2013. However, she was later ruled out for a significant amount of the season after suffering a deep cut to the leg in the carpark following a match in the 2013 AFC U-19 Women's Championship.

Perth Glory FC

Arnold returned to Perth Glory in August 2014. Arnold was approached to switch codes and play Australian rules football in the newly formed AFL Women's in 2016, but chose to remain in soccer.

Brisbane Roar FC

In October 2016, Brisbane Roar announced that they had signed Arnold.

Arna-Bjørnar

In March 2018, she signed with Arna-Bjørnar in the Toppserien.

Chicago Red Stars

In July 2019, she signed for the Chicago Red Stars, in the NWSL, but made no appearances.

West Ham United

On 9 July 2020, Arnold signed for English club West Ham United of the FA Women's Super League, where she was appointed the team's captain in 2023. On 18 April 2021, Arnold was handed a surprise 20-minute cameo in midfield during an 11–0 win over Chichester & Selsey in the fourth round of the Women's FA Cup. In May 2024, she was voted Women's Hammer of the Year by West Ham United supporters for the 2023–24 season.

Portland Thorns FC

On 10 July 2024, Portland Thorns FC, an American professional women's soccer team based in Portland, announced that they had…

Arnold received her first call-up to the Australian national team for a tour of the United States in 2012. She made her debut in November that year, keeping a clean sheet in a win over Chinese Taipei in the 2013 EAFF Women's East Asian Cup preliminary round 2. Arnold began to feature regularly in national squads in 2013, with previous incumbent goalkeepers Melissa Barbieri and Lydia Williams unavailable. Following their returns, Arnold was not included in the national setup for some time, before returning for the 2015 Cyprus Cup in March 2015. Arnold was included as one of three goalkeepers in the Matildas squad for the 2015 World Cup in Canada. She was selected in the Australia squad for the 2016 Summer Olympics as one of two goalkeepers in the squad along with Lydia Williams, and played one match in the tournament, a group stage win over Zimbabwe. Arnold was named to the Matildas squad for the 2019 World Cup in France. Arnold was a member of the Matildas Tokyo 2020 Olympics squad. The Matildas qualified for the quarter-finals and beat Great Britain before being eliminated in the semi-final with Sweden. In the playoff for the Bronze medal they were beaten by the USA. Arnold is a member of the Matildas 2023 FIFA Women's World Cup squad, goalkeeping for all of Australia's Group B matches. She was named player of the match after saving three spot kicks in the quarter-final penalty shoot out to see the Matildas progress to the final four for the first time. This led to many…

Mackenzie Arnold was born to Steve and Leah Arnold and raised with an older sibling on the Gold Coast. Her sibling is profoundly deaf and wore hearing aids since being a toddler. In 2020, during the COVID-19 pandemic, Arnold acknowledged that she also has significant hearing loss and subsequently wears hearing aids off the pitch. In 2023, she partnered with Audika, a hearing clinic and service provider in Australia, to tackle the stigma of hearing loss. Arnold played junior football for Burleigh Heads as well as Robina City and attended St Andrews Lutheran College for primary school, Palm Beach Currumbin State High School for secondary and completed a Certificate 4 in Fitness at Gold Coast TAFE (2013–2015).

Arnold dated Scottish footballer Kirsty Smith between 2022 and 2024 while they both played for West Ham. Arnold supports the Brisbane Broncos in the National Rugby League (NRL).