D.C. Council member David Grosso (I-At Large) was among those voting against the Corizon health-care contract for the city jail, calling the company “scandal prone.” (Astrid Riecken/For The Washington Post)

The D.C. Council on Tuesday rejected a controversial health-care contract proposed for the city’s jail after weeks of fierce arguments and heavy lobbying by supporters and opponents.

The council’s 6-to-5 vote against a $66 million proposal by Corizon Health marked a high-profile defeat for Mayor Muriel E. Bowser (D), who had supported the contract.

Bowser spokesman Michael Czin and Corizon chief executive Woodrow A. Myers Jr. said they were disappointed in the decision. Czin said it will force the District to spend more on inmate medical services in the short term while a new bidding process is conducted.

Contract opponents cast the decision as a victory for inmate care and a rejection of a company mired in legal troubles in other states, including several high-profile wrongful-death lawsuits.

“I am happy that the council stood up for the most vulnerable residents in D.C.,” said Deborah Golden, who heads an inmate advocacy arm of the Washington Lawyers Committee for Civil Rights and Urban Affairs. “I think Corizon has a record of shoddy and unconstitutional care across the country,” she added.

Golden said she hopes Tuesday’s decision will “start a conversation” about how best to provide for the District’s inmates, who suffer from a higher rate of illness than the wider population. “There are issues with the current contractor and contract, and that needs to be addressed,” she said.

Bowser and other supporters on the council said they backed Corizon, which had beaten three other bidders during an 18-month procurement process, because it was the most qualified provider — and because it was important to respect the city’s independent bidding system.

Corizon and its opponents pressed council members aggressively in the weeks leading up to the vote, raising questions about the impact of money and lobbying on council decisions and provoking emotional allegations.

The opposition had forced then-Mayor Vincent C. Gray (D) to withdraw the contract from consideration last December. This year, Bowser chose to revive the proposal rather than reopen the bidding process.

A heated debate on the dais preceded the vote Tuesday, with council members on each side growing visibly exasperated with the other side’s arguments.

David Grosso (I-At Large) said that if getting the best possible care for the city’s inmates is the objective, then “contracting with a for-profit, scandal-prone company is not the way for us to get there.”

Council Chairman Phil Mendelson (D) and members Mary M. Cheh (D-Ward 3) and Elissa Silverman (I-At Large) also delivered strongly worded criticisms of Corizon’s record in other states and of the procurement process that resulted in Corizon’s win.

“Switching to Corizon is a mistake. And if we do not vote for this amendment to disapprove, we will rue the day,” Mendelson said.

Contract supporters Vincent B. Orange (D-At Large) and Jack Evans (D-Ward 2) said that rejecting Corizon would keep in place an expensive contract that needs to go.

The current contract holder, Unity Health Care, lost out to Corizon in the latest bidding despite making a lower bid and having strong support among advocacy groups and some council members.

Unity has provided health care in the city’s detention centers for seven years and provides low-cost medical service in clinics throughout the city.

“Say we don’t approve this contract. Say Corizon is voted down. Where does that really leave us?” Evans said. “Would they both compete again? And what if Corizon were to win again?”

Evans also challenged his opponents on the council to scrap the competitive bidding process and “just sole-source the contract to Unity” since they apparently had already decided which company they wanted. “Ridiculous,” Evans added.

Despite its higher bid, Corizon earned Bowser’s support in part because of its plans for providing mental-health services, Czin said.

Both companies accounted for the city’s shrinking inmate population by offering per-capita prices that would have saved the city money over the current contract, under which Unity is paid a higher, fixed rate that is not tied to inmate population.

Continuing that arrangement while the District restarts the bidding process will cost roughly $2.4 million more than was envisioned in Bowser’s proposed 2016 budget, Czin said.

Orange delivered impassioned arguments and handed out the names of council members, including Grosso and Silverman, who had previously supported a bill that would bar the council from voting on city contracts such as this one.

“These seven council members said that the council should not be in the process of contract review when it has gone through a competitive process, and I hope they will stay true to form,” Orange said.

Orange also accused his adversaries of carrying a bias for Unity.

“Don’t think that Unity doesn’t have relationships up on this dais,” he said.

Ultimately, the deciding vote Tuesday belonged to freshman lawmaker Brianne K. Nadeau (D-Ward 1), who voted against Corizon along with Mendelson, Charles Allen (D-Ward 6), Cheh, Grosso and Silverman.

Council members Yvette M. Alexander (D-Ward 7), Anita Bonds (D-At Large), Evans, Kenyan R. McDuffie (D-Ward 5) and Orange voted for Corizon.

Nadeau did not speak during the debate but issued a statement afterward.

“The process produced an unacceptable result that would entrust the care of some of our most vulnerable residents to a company with a deeply troubling track record of human rights abuses,” she said.

“Corizon Health is deeply disappointed, not solely for our company, but also for the District,” the company’s chief executive, Woodrow A. Myers Jr., said in a statement Tuesday. “We have been committed to the possibility of serving Washington, D.C., for over five years.”

McDuffie said he was aware of Corizon’s legal troubles but had consulted nearby correctional facilities in Maryland and Virginia and decided to support the contract.

McDuffie emphasized the independence of the city’s procurement process, handled by the Office of Contracting and Procurement, and promised that if Corizon was found to provide bad health care, “I’ll roll out the red carpet for the civil rights division to come in and have a look at what’s going on.”