Gwen O’Shea, the longtime leader of the Health and Welfare Council of Long Island, will leave the human services nonprofit in March for the top post at the Community Development Corporation of Long Island, both agencies announced Thursday.

O’Shea has worked at the Melville-based council for 15 years — the last 10 as its president and chief executive.

The Health and Welfare Council is in its 70th year of operation and focuses on increasing access to health care, improving people’s economic and nutritional security, and promotes regional planning through its work with 300 member agencies. CDCLI, a 48-year-old agency based in Centereach, works to provide affordable housing opportunities for low- and moderate-income people.

O’Shea is slated to become president and CEO of the housing agency, on March 27 — three days after she leaves her current position at the council.

On Thursday, council officials and others lauded O’Shea, 40, for her effectiveness in raising awareness about the needs of Long Island’s poor, and in addressing their concerns by bringing together experts, policymakers, advocates and service providers to help at-risk Long Islanders.

John Imhof, Nassau County Department of Social Services commissioner, called O’Shea a “consummate professional” who “builds consensus to work out issues.”

Bob Detor, chairman of the Health and Welfare Council’s board of directors, will take over as interim director of the council as the board looks to replace O’Shea.

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“I think she’s brought a tremendous amount of professionalism to the agency,” Detor said in an interview. “She has pushed us to identify those areas where something needed to be done and no one was stepping in. Superstorm Sandy was one example.”

Under O’Shea’s leadership, the council used its “unmet needs roundtable,” which brought together donors and community-based organizations to help Sandy victims — an effort that yielded “more than $10 million in financial support to Long Island individuals and families struggling with their disaster recovery,” Detor said in a statement.

JoAnn Smith, one of the council’s two vice chairs, called O’Shea’s impending departure “bittersweet.” Nevertheless, she praised O’Shea’s talents, calling her a “visionary” and effective leader.

Jim Coughlan, board chairman of CDCLI, said O’Shea was selected to replace the agency’s longtime leader, Marianne Garvin, after a national search. He said O’Shea’s Long Island experience and “proven track record with many of our stakeholders and many of our constituents” won out. “We’re very happy,” he said.

On Thursday, O’Shea praised the “tremendous board and committed staff” of the council she leaves behind, and said she said she was “excited to build off the accomplishments of Marianne.”

Garvin, who announced her plans last April to retire after 25 years with the housing agency, said she supported O’Shea’s selection. Until superstorm Sandy in 2012, she only knew O’Shea by reputation, Garvin said.

“When superstorm Sandy hit, it was pretty traumatic for me personally and as an organization,” Garvin said. “We were a housing organization and many people in the community and our partners turned to us to say, ‘What are you going to do to help people?’ It wasn’t an option, so we became a disaster recovery agency.”

Garvin said O’Shea’s efforts after Sandy were “critical” in ensuring resources were directed to those who needed them the most.

“Her ability to bring hundreds of nonprofits and others together shows her remarkable leadership ability,” she said.