In Bill de Blasio’s City Hall, it seems more and more, there is only a left wing.

The mayor, who advanced in politics by grass-roots organizing, has built a team filled with former activists — figures more accustomed to picketing administrations or taking potshots from the outside than working from within. His administration is heavily populated with appointees best known for the fights they have fought.

On Friday, Mr. de Blasio appointed Steven Banks, who is the attorney in chief of the Legal Aid Society and a longtime critic of city policies affecting low-income residents, as commissioner of the city’s Human Resources Administration. Mr. Banks recently praised the new mayor for transferring hundreds of children and their families from two homeless shelters cited for violations that made the facilities unfit and unsafe for children.

Mr. Banks has spent his career facing off with city government at public meetings and in the courts. But he is embraced in a de Blasio administration.

“We’ve said all along, as we make appointments, our standards are clear,” Mr. de Blasio said in announcing the appointments of Mr. Banks, who once lost to him in a City Council race, and two other officials. “We need people who share our progressive values related to the future of this city.”