Kennedy debuted for the Matildas against New Zealand in 2012. In 2014, at age 19, she was named to the Matildas squad for the 2014 AFC Women’s Asian Cup. She appeared in three games, as Australia finished Runner-up to Japan.

Kennedy started her W-league career playing for Sydney FC in the 2010–11 season, where she featured in 3 games. The following year, Kennedy switched clubs and joined the Newcastle Jets in the 2011–12 W-League before returning to Sydney FC in the 2012–13 season. For the 2013–14 season, she joined city rivals Western Sydney Wanderers. and in the 2014 season she joined Perth Glory. In 2015, she returned to Sydney FC and would remain there the following 2 seasons. In 2016, Kennedy signed with the Western New York Flash in the National Women’s Soccer League. She appeared in 17 games for the Flash in 2016. Kennedy played every minute of Western New York’s two playoff games, as the Flash won the 2016 NWSL Championship.

In May 2015, Kennedy was named to Australia’s 23-player roster for the 2015 FIFA Women’s World Cup and was the second youngest player on their roster. Kennedy appeared in all five matches for Australia. The Matildas finished second in their group and advanced to the knockout stage. They defeated Brazil in round 16 but lost to Japan in the quarter-finals.

Kennedy attended her first Olympic Games in 2016. She played every minute of Australia’s four matches at Rio 2016. Their quarter-final match against Brazil was tied 0–0 after extra time and went to penalties. Kennedy was the final penalty taker for Australia; she did not score her penalty and Brazil won the match 7–6 on penalties.

On 19 January 2017 Kennedy was traded to the Orlando Pride in exchange for midfielder Sam Witteman. She appeared in every game for the Pride in 2017. In the final game of the regular season on 30 September, Kennedy scored the game-winning goal on a free kick in stoppage time. This win allowed Orlando to finish the regular season in 3rd place and qualify for the playoffs for the first time in club history. In the semi-final, Kennedy scored again but Orlando lost 4–1 to the Portland Thorns.

In the 2018 NWSL Season, Kennedy appeared in 20 games and scored 2 goals; however, Orlando could not repeat their success of 2017 and finished outside the playoffs.

At the 2018 AFC Women’s Asian Cup Kennedy scored two goals for Australia. The second goal she scored was a stoppage time equalizer against Thailand in the Semi-final. Australia went on to win the game in penalties. Australia lost to Japan 1–0 in the final.

After spending one season at Melbourne City, Kennedy signed with Sydney FC for the 2018–19 W-League season, returning to the club she had played at for four previous seasons. On 16 February 2019 Kennedy won her third W-league Championship title with a 4–2 win over Perth Glory in the grand final. She re-signed with Sydney FC for the 2019–20 season. The team returned to the grand final in 2020 but lost to Melbourne City 1–0.

In May 2019, Kennedy was named to the Matildas squad for the 2019 FIFA Women’s World Cup, the second time she was included in a World Cup squad. At the World Cup, Kennedy started all four of Australia’s matches. In the Round of 16 tie against Norway, Kennedy received a straight red card in the 104th minute of extra-time for a DOGSO foul on Lisa-Marie Utland. Australia went on to lose on penalties and were eliminated.

In March 2020, the impending NWSL season was postponed due to the coronavirus pandemic. An eventual restart was made through a smaller schedule 2020 NWSL Challenge Cup tournament. However, on 22 June, Orlando withdrew from the tournament following positive COVID-19 tests among both players and staff.

In August, having been unable to feature for Orlando Pride in 2020, Kennedy moved to English FA WSL club Tottenham Hotspur on loan ahead of the 2020–21 season.

On 12 November 2020, while on loan at Tottenham, Kennedy was acquired by Racing Louisville FC in the 2020 NWSL Expansion Draft.