Solicitor Alistair Smith from Ison Harrison, said his company were representing 200 families and individuals who wanted to be involved in the public inquiry.
He said he was “tremendously pleased” a chair had been appointed.
“This is what the families have been campaigning for so long. This is a good moment and we now have movement.”
He said while the inquiry would formally begin on Monday, it could be some years before the actual hearings start.
Chief executive of TEWV, Alison Smith, said they welcomed the appointment of the inquiry chair “as an important step forward”.
“We acknowledge the significance of this moment for the families and loved ones involved, and we continue to hold them in our thoughts,” she said.
“We will co-operate fully with the public inquiry with honesty, openness and humility. We are truly sorry for the times when care fell short, and are committed to listening, learning and continuing to improve.”
Lawyers representing those affected previously said they were told an inquiry chair would be appointed by the end of February, along with the terms of reference.
The DHSC said the appointment followed 159 new NHS mental health facilities across England, backed by £343m in funding.
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