Mark-Viverito was born in San Juan and grew up in Bayamón, Puerto Rico. She came to New York at age 18 to attend college, earning a BA degree from Columbia University in 1991 and then a Master of Public Administration degree from Baruch College in 1995. Her hyphenated last name comes from her late father, Anthony Mark, and the maiden name of her mother, Elizabeth Viverito. Her father was a doctor and a founder of San Pablo Hospital in Bayamón, where her mother still lives.
Before running for City Council, Mark-Viverito served as a member of Community Board 11, coordinator of the movement Todo Nueva York con Vieques, president of Mujeres del Barrio, and Strategic Organizer for Local 1199 of the Service Employees International Union (SEIU), an influential health care workers union.
In August 2014, Mark-Viverito publicly disclosed that she was infected with the most common STD, the human papillomavirus. She is not married.
Mark-Viverito campaigned in solidarity with the Occupy Wall Street movement and identified herself as part of the "99%" of income earners despite having a net worth in the millions. She and her family inherited an estimated $6,700,000 in holdings from her father who was a doctor. Prior to her inheritance, she applied for a tax payer subsidized interest loan in 1998 when her property at the time was worth $310,000. As of 2014, the multi-story condominium property was worth around $1,300,000. Mark-Viverito rents out her properties, but did not report her rental income. Her spokesman claimed it to be an honest oversight on her part.
After running unsuccessfully against Phil Reed for City Council in District 8 in 2003, Mark-Viverito was elected to the position when Reed reached his term limit in 2005. During her first four years in office, Mark-Viverito sponsored and passed several pieces of legislation regarding tenant harassment, building safety, greening buildings, and park conservancies. In January 2009, she criticized the voting record of newly appointed New York Senator Kirsten Gillibrand on immigration.
During Mark-Viverito's second term in the Council, she served as chair of the Parks and Recreation Committee and as founding co-chair of the Progressive Caucus.
In November 2013, she won re-election to her third term in the Council, and her close ally Bill de Blasio was elected mayor. Soon the New York Daily News cited Mark-Viverito as "the front-runner" for "New York City's second-most powerful political post — Speaker of the City Council." A grassroots effort to boost her Speaker candidacy included social media, fliers, phone banking, and volunteer recruitment.
Mark-Viverito was elected City Council Speaker on January 8, 2014, at age 44, becoming the first member of the Council's Black, Latino and Asian Caucus to hold this position. Her first "State of the City" speech emphasized reform of the criminal justice system.
In January 2016, Mark-Viverito introduced a collection of eight bills known as the "Criminal Justice Reform Act" to reduce the penalty for acts such as violating park rules, littering and public urination from misdemeanors to the civil process. Mark-Viverito sponsored the bills so that young people in communities of color could "fulfill their potential" by incentivizing officers to give verbal warnings and fines but not remove the option of making arrests.
In 2017, Mark-Viverito declined to boycott the Puerto Rican Day Parade, after organizers decided to honor Oscar López Rivera, a prominently incarcerated member of Fuerzas Armadas de Liberación Nacional Puertorriqueña (FLAN).