Ms Denyer visited Brighton earlier this week to congratulate Sian Berry on her selection as the next Green parliamentary candidate for Brighton Pavilion.
Ms Berry will replace Caroline Lucas, who is standing down as an MP at the next election.
The Green co-leader, who is running for election in Bristol Central, said she is hopeful that Brighton will re-elect a Green MP next year, but that the party “never takes any voters for granted”.
She said: “I think Sian’s very long track record with the party and as an elected representative on the London Assembly and as a councillor has shown that residents of Brighton Pavilion can have high expectations and they’ll be met.”
Ms Denyer addressed the party’s result in the local elections, which saw their number of councillors in Brighton and Hove shrink from 20 to seven.
She said the local party is reflecting on the results and why residents voted the way they did.
“I know the seven Green councillors that were elected are already working really hard for their residents, representing them on the council and asking questions and making proposals to the Labour administration.
“Of the seats we held on the city council, they were all in Brighton Pavilion, so I think there are still a lot of people who support the Green Party, as well as those who voted Labour in the locals but who are open-minded to voting Green again in the future.
“We don’t take any votes for granted and we absolutely need to go out on the doorsteps and have conversations with those people and find out what motivates them and what they want to see from their local MP.”
Caroline Lucas was elected as the Green Party’s first MP in 2010, but the party has yet to repeat that success anywhere else in the country.
While Ms Denyer acknowledges the difficulty the electoral system poses for smaller parties to break through, she also pointed to the success of sister Green parties in Australia and Canada – both of which also have a similar voting system.
She said: “In both of those countries, they were bumping along on just one Green MP for several successive elections, basically the same situation to us here, and then in recent general elections, they jumped up to three or four.
“Even though the chips are stacked against us, we can still win under first past the post.”
Brighton Pavilion is expected to be a closely fought race, with Labour anticipated to try and take the seat following success in the city-wide local election.
However, Ms Denyer said that voters in the city, much like those in Bristol, may opt for a more progressive voice in Parliament.
She said: “I think, for the vast majority of voters in Bristol Central and in Brighton Pavilion, their ideal situation would be a Labour government with a handful of Green MPs to pull them in a progressive direction.
“Voters in Brighton are very switched on to what’s happening in national politics and it’s similar to where I am as a candidate in Bristol. People do bring up on the doorstep that they are perhaps lifelong Labour voters but they’re disappointed by the direction that Keir Starmer is taking the Labour Party in.
“That’s where we, as a Green Party, have something really valuable to offer, because a handful of Green MPs can pull Labour in a more progressive direction on everything from workers’ rights to rent controls.
“In the Green Party, we have a phrase: ‘A Green in the room changes everything.’
“Every time a new Green gets elected onto a council, we’re reminded how much that is true – nowhere more so than in Westminster with Caroline.
“Having a small handful of Greens in Parliament means that questions get asked and proposals made that simply wouldn’t be made otherwise.”
In a message to Brighton voters, Ms Denyer asked: “What would you rather see on the day after the next general election – a 100 per cent Labour government, where Starmer can do as he wants with no challenge from the left, or a Labour government with a handful of Green MPs pulling them in a progressive direction?”
The next general election is expected to take place sometime next year, with political pundits speculating that voters could be called to the polls in May or in the autumn.
At the last election in 2019, Caroline Lucas held Brighton Pavilion for the Green Party with a majority of almost 20,000 votes.