More recently, he led the charge to repeal 50-A and the gay panic defense and authored legislation making all public, single-occupancy bathrooms gender-neutral.

[3] O'Donnell first ran for the legislature in 1998, making an unsuccessful bid for the New York State Senate in the 30th district; he lost the Democratic primary to Eric Schneiderman.

[10] In 2008, O'Donnell was considered by New York Governor David Paterson to fill the Senate vacancy created by the appointment of Hillary Clinton as President Obama's Secretary of State.

[17] O'Donnell was the prime sponsor of the Dignity for All Students Act, one of the first laws in New York history to explicitly include protections based on gender identity and expression.

[18] In 2019, New York enacted his legislation to ban the so-called gay and trans "panic" defense, which asks a jury to find that a victim's sexual orientation or gender identity is to blame for a defendant's violent reaction, including even murder.

The law repeals 50-a in its entirety – allowing individuals, lawyers, and the press to request police disciplinary files that have long been held in secret.

[citation needed] Additional legislative victories include: successfully lowering NYC speed limits to 25 mph; expanding sexual harassment protections to unpaid interns; mandating mental health discharge plans for incarcerated individuals; and passing the Domestic Violence Escalation Prevention Act, which bans individuals convicted of domestic violence from owning any type of firearm.

[citation needed] Assemblyman O'Donnell announced that he will not seek reelection to the New York State Assembly in November 2023 and will retire from election politics in January 2025.

The bill (sponsored by Assemblymember Amy Paulin) being debated was regarding police officers seizing guns owned by suspects during domestic violence situations.

The ceremony and reception were attended by over 400 people including Governor Andrew Cuomo, Assembly Speaker Sheldon Silver, Comptroller Tom DiNapoli, Attorney General Eric Schneiderman, New York City Council Speaker Christine Quinn, many of his colleagues from the Assembly and State Senate, family, and friends.