Caral Ni Chuilin has been appointed interim Communities Minister after Deirdre Hargey stepped aside for health reasons.
Ms Hargey said she had been admitted to hospital and would undergo surgery in the coming days.
She said she hoped to resume her ministerial duties "in a number of weeks".
A former Sinn Fein Lord Mayor of Belfast, Ms Hargey was co-opted as an MLA for South Belfast last December, replacing Mairtin O Muilleoir, and appointed to the Executive the following month.
Ulster Unionist leader Steve Aiken was among those to send well-wishes last night.
He tweeted: "Sorry to hear this news - @uuponline wish @DeirdreHargey a speedy recovery and look forward to seeing her back in @niassembly soon."
Alliance leader Naomi Long posted: "Sending best wishes to @DeirdreHargey for her surgery and recuperation. Hope you'll be back to full health soon."
Announcing her decision to temporarily step aside, Ms Hargey referred to "exceptional personal circumstances".
She said: "I have informed joint head of government Michelle O'Neill and my party president Mary Lou McDonald that I will be stepping aside from my role as Minister for Communities temporarily for health reasons.
"Due to illness I have been admitted to hospital, and am to undergo surgery in the coming days, which will require time to properly recover. In light of these exceptional personal circumstances I am unable in the short-term to discharge my ministerial duties, or participate fully in the Executive committee.
"I have also written to joint heads of government Michelle O'Neill and Arlene Foster to inform them of my decision to stand aside from my ministerial post. I look forward to being able to resume ministerial responsibilities in a number of weeks following my treatment and recovery."
Mrs O'Neill said: "I want to wish my colleague Deirdre Hargey a full and speedy recovery and thank her for the excellent work she has done in her ministerial role to date.
"I look forward to her returning to that post on her recovery and hope she will be back behind her desk as soon as possible.
"I am appointing Caral Ni Chuilin as Minister for Communities on a temporary basis until Deirdre Hargey's return.
"I wish Caral well and know that she will bring a wealth of experience, determination and dedication to the post."
Ms Ni Chuilin previously served as Minister for Culture, Arts and Leisure from May 2011 to May 2016.
She has been a Sinn Fein MLA for North Belfast since 2007.
The Department for Communities covers a wide brief, including housing, benefits and pensions, sport, culture and languages.