Alliance North Antrim MLA Patricia O'Lynn has announced her resignation.
The 33-year-old will leave her role at the end of March to take up a new position at Queen's University Belfast.
In a statement announcing her departure, Ms O'Lynn said the ongoing impasse at Stormont has been "frustrating".
Read more: DUP silent on speculation of discontent over handling of Protocol talks with PM adviser
Ms O'Lynn was elected in North Antrim last May, becoming the first female MLA and first Alliance MLA for the constituency.
She was the fifth and final person elected in the area after a surge of transfers saw her overtake DUP stalwart Mervyn Storey.
Her win secured Alliance a historic victory at the expense of the DUP in party founder Rev Ian Paisley's North Antrim heartland.
Ms O'Lynn was also previously a councillor on Mid and East Antrim Borough Council and a special adviser to Alliance leader Naomi Long when she was Justice Minister.
In a statement, Ms O'Lynn said: "It has been an honour to serve the people of North Antrim as their MLA and previously the people of Ballymena as a councillor. My only regret is I was not able to do so in the Assembly chamber itself due to the ongoing impasse, which has proved frustrating.
"Nevertheless, it has been a privilege and I will continue representing my constituents fully while I remain in the role. I thank every person who voted for me and for Alliance locally in previous years and assure them they will continue to be represented by my successor.
"I wish to pay tribute to my Alliance colleagues, party members and also my staff, who have worked hard for people right across the constituency. There is an exciting amount of talent emerging through the North Antrim Alliance Association, which continues to grow in numbers.
"The party continues to have my full support and I look forward to supporting whoever succeeds me as MLA. The people of North Antrim proved last May they want to see Alliance's positive message of inclusion and I am confident that will continue. I look forward to supporting whoever succeeds me as MLA."
Alliance leader Naomi Long described Ms O'Lynn as "both a colleague and a friend".
The East Belfast MLA added: "It is a huge loss not only to the party and the Assembly but especially for the people of North Antrim, who have lost a fearless and passionate representative on the issues that matter to them.
"It is undoubtedly a difficult and uncertain time for many in politics due to the ongoing impasse. Patricia will be hugely missed but I am confident Alliance will continue to build on its recent superb results across North Antrim and on the sterling work Patricia has carried out as an advocate for a united community there.
"On behalf of myself and the entire Alliance team, I wish her every success and happiness in her new role."
For the past year the DUP has been blocking Stormont power-sharing in protest against Brexit's Northern Ireland Protocol.
The party has refused to restore the Executive and Assembly until significant changes are made to the contentious Irish Sea trading arrangements.
Civil servants are currently running public services in Northern Ireland in the absence of elected ministers.
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