Leader of the Greens (2020–2025)
On 3 February 2020, Richard Di Natale announced his resignation as leader of the Greens and imminent retirement from politics, citing family reasons. Bandt announced his candidacy for the leadership shortly after. On 4 February, he was elected unopposed. Larissa Waters was elected unopposed as co-deputy, with Nick McKim defeating Sarah Hanson-Young and Mehreen Faruqi to become the second co-deputy. Bandt has been described by the political journalist Paddy Manning as the first Greens leader from the Left wing of the party.
During his leadership of the Greens, Bandt focused the party's energy towards campaigning for an Australian Green New Deal, to address what he refers to as a "climate and environment emergency." According to Bandt, it would involve the "government taking the lead to create new jobs and industries, and universal services to ensure no one is left behind." Bandt also focused on relations between his party and regional communities with the intent of visiting mining townships and farmers across Australia, arguing that his party is "the only one" trying to stop climate change from "devastating agriculture". He has adopted a pro-mining message, but with a focus on expanding the lithium industry and other minerals necessary for a zero-carbon economy; rather than using coal. Under Bandt's vision, the party aspired to develop a power-sharing situation with a Labor government at the 2022 election, similar to the Gillard era.
Whilst serving as party leader, Bandt also acted as the Greens' spokesperson for: the Climate Emergency, Energy, Employment & Workplace Relations, and the Public Sector.
In the 2022 federal election, Bandt retained his seat in Melbourne with a primary vote of 49.6%, beating that of his previous election. However, there was a 12.4% swing against him in the two-candidate-preferred vote. The Greens gained three further seats in the House of Representatives and three in the Senate, with an increase in the first-preference vote by 1.9% to 12.3%.
On 19 June 2022, Bandt had the Australian flag removed from behind the podium at a media conference of his, saying that it "represented lingering pain" for some Australians. His action received varied responses, including condemnation, with newly elected Prime Minister Anthony Albanese stating that Bandt should "reconsider his position and work to promote unity and reconciliation."
On 9 September 2022, one day after the death of Queen Elizabeth II, Bandt tweeted "Rest In Peace Queen Elizabeth II. Our thoughts are with her family and all who loved her. Now Australia must move forward. We need Treaty with First Nations people, and we need to become a Republic."
Bandt led the Greens into the 2025 election and saw the Greens lose all but one of their seats in the House of Representatives. Bandt himself lost his seat in the division of Melbourne following a 5.27% decrease in his primary vote and a 8.60% swing against him on a two candidate preferred basis to the Labor Party's candidate Sarah Witty. Following the poor results for the Greens, Bandt resigned as leader of the party. He considered running for the seat again but felt "you have to be more than fully committed to do that, and I've climbed that mountain. I just can't see it now".