Ms Patten will leave parliament after eight years as a Member for the Northern Metropolitan Region and called the election result disappointing.
"I'd like to congratulate the successful candidates for the region and indeed all successful candidates in the November 26 Victorian election," she wrote in a statement on Monday.
"Sadly, I will not be joining them in the 60th parliament. But I do have some homework for them.
"While the official result is disappointing for me, it has been such an uplifting, enlightening privilege to serve the voters of this vast and diverse population, and to have achieved progressive change. I certainly won't die wondering."
While final results for the Legislative Council are not yet known, it appears Labor and the coalition will claim 15 seats.
Former disgraced Labor minister turned Democratic Labour Party hopeful Adem Somyurek could win Ms Patten's seat, however official results won't be made known until Tuesday.
Mr Somyurek said it was too early to claim victory.
"Whilst it's gracious of candidates to concede before the counting is concluded I'd urge caution," he tweeted on Monday.
"LC counts are complex. Every point of elimination may throw up surprises which change the dynamic of a count. I'll wait till the button is pressed before I claim victory."
The crossbench is likely to be made up of 10 mostly left-leaning members, including three Greens and seven candidates from micro parties.
Among them are three potential candidates from Legalise Cannabis Victoria, one from the Shooters, Fishers and Farmers, one from the Animal Justice Party and one from the Liberal Democrats.
Premier Daniel Andrews led Labor to a sweeping victory to secure a third term in power.
Ms Patten was first elected to Victorian parliament in 2014 and re-elected in 2018
Throughout her two terms in parliament, Ms Patten championed social reform including Anti-vilification legislation and also led an inquiry into Voluntary Assisted Dying laws.
She served as Chair of the Legislative Council Legal and Social Issues Committee and advocated for a medically supervised injecting centre in North Richmond.
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