The West Tyrone MLA will join Alex Attwood at the negotiating table while Dolores Kelly will take Mr McDevitt's place at the Policing Board.
The former South Belfast MLA stepped down last week after acknowledging that he had not declared some payments.
SDLP leader Alasdair McDonnell said: "Joe will provide a strong voice for ordinary people whose lives are so negatively affected by on-going conflict and contentious parades."
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com