Baltimore Mayor Catherine Pugh has resigned amid investigations into lucrative business deals for her self-published children's books.
The resignation follows an FBI raid of her home and an amendment proposed by Baltimore City Council that would make it possible to remove her from office.
The Democrat earned thousands of dollars through sales of Healthy Holly books to city-linked public entities.
They include health providers and schools.
Ms Pugh has been on sick leave since 1 April, recovering from pneumonia, according to her office.
She announced her resignation on Thursday in a statement read by her lawyer, Steve Silverman.
"I am sorry for the harm that I have caused to the image of the city of Baltimore and the credibility of the office of the mayor," the statement said.
Earlier in April, Maryland's Republican Governor Larry Hogan and most of Baltimore City Council urged Ms Pugh to quit.
Ms Pugh's decision to step down marks a change in course for the mayor.
On 8 April, Ms Pugh's office released a statement saying she would resume duties after her health had recovered.
Baltimore City Council President Bernard "Jack" Young, who has been serving as acting mayor, will take over Ms Pugh's post until the next election in 2020.
The FBI confirmed to CBS News, the BBC's US affiliate, that it was working with the Internal Revenue Service (IRS), America's tax-collection agency, on the inquiry into Ms Pugh's book sales.
Official sources say the mayor's deals for Healthy Holly books - which promote healthy eating and exercise - are part of the inquiry, but there is "more to the picture".
The federal investigation has been ongoing for more than a year, law enforcement sources told CBS.
Ms Pugh received $500,000 (£388,000) from the University of Maryland Medical System (UMMS) for 100,000 copies of the books that would go to schools while she was on the hospital system's board, the Baltimore Sun reported.
Kaiser Permanente, another health provider, later revealed it paid over $100,000 for 20,000 copies of the books while it was negotiating a contract to become the medical insurance provider for Baltimore city employees.
Ms Pugh has called the book deal with the university medical system "a regrettable mistake" and later resigned from the board.
She is the second Baltimore mayor in the past decade to leave office while facing allegations of corruption.
In 2009, former Mayor Sheila Dixon was found guilty of misdemeanour embezzlement and was forced to resign.
Dixon ran for office again in 2015 and lost, to Ms Pugh.