On March 15, 2016, Sittenfeld lost the Senate Democratic primary election to former Ohio Governor Ted Strickland.

[5] On July 12, 2020, Sittenfeld announced that he would run in the 2021 Cincinnati mayoral election,[6] but dropped out of the race following his arrest on political corruption charges.

[10] Sittenfeld accepted $40,000 in bribes from undercover FBI agents posing as real estate investors in exchange for votes on a matter before the city council.

[11] On July 8, 2022, following a two-and-a-half week trial in U.S. District Court in Cincinnati, Sittenfeld was convicted on two felony counts of bribery and attempted extortion and was sentenced to 16 months in prison on October 10, 2023.

[16] Sittenfeld's father, Paul, started his career at Procter & Gamble, before leaving to work at Planned Parenthood, later running the Cincinnati Fine Arts Fund, and finally transitioning to become a family investment advisor.

[32] In 2020, Sittenfeld sponsored the first "renter's choice" legislation in the United States, allowing apartment-renting tenants alternatives to cash security deposit.

[34] Sittenfeld later introduced legislation allowing prospective job-applicants to the City of Cincinnati with prior marijuana possession charges on their records to not be denied employment.

[35] In 2020, with councilmember Greg Landsman, Sittenfeld introduced legislation to move toward a policy of citations to court, instead of arrests, for low level offenses.

[36][non-primary source needed] Sittenfeld sponsored legislation creating Cincinnati's first-ever bus-only lane to provide dedicated avenues for Metro buses to traverse city streets, with an emphasis on the Central Business District, to reduce congestion and improve travel times.

[38] Beginning in 2017, Sittenfeld began an effort with councilmember Chris Seelbach to establish an annual commitment in the city's budget directing $500,000 toward city-wide pedestrian safety improvements.

In 2019, that allocation funded 70 projects, such as enhanced lighting and signs, improved crosswalks, and "bump-outs" which reduce the width of streets at key, pedestrian-heavy intersections.

[39] Sittenfeld sponsored city funding for a new health and wellness center in the neighborhood of Evanston, which serves immigrant students and families.

[43][44] In 2018, Sittenfeld was caught leading the "Gang of Five", a group of five city council members (Sittenfeld, Chris Seelbach, Greg Landsman, Wendell Young, and Tamaya Dennard) who communicated via secret text messages attempting to undermine the mayor and bypass public meetings and debates.

[45] In March 2019, the Gang of Five agreed to turn over their text messages in order to settle a lawsuit filed by a local anti-tax activist.

[48] In June 2019 additional text messages were released as a result of a lawsuit filed by Sinclair Media reporter Angenette Levy in which it was revealed that Sittenfeld encouraged the then-city manager, Harry Black, to work with African American community leaders to avoid being fired.

[54] On November 19, 2020, Sittenfeld was arrested by federal agents on charges of accepting bribes in exchange for favorable votes on developmental deals.

[61] On January 28, 2016, Sittenfeld announced a proposed amendment to the Ohio legislature to restore home-rule authority on gun control.