SINN Féin has co-opted Áine Murphy to fill the Stormont vacancy left by the departure of Seán Lynch.
Ms Murphy's will join Jemma Dolan and Colm Gildernew as one of the party's three representatives in Fermanagh and South Tyrone.
Her co-option is the ninth by Sinn Féin during the current mandate, meaning one-third of the party's 27 MLAs were not personally elected at the polls.
At 26, Ms Murphy is thought to be the youngest representative at Stormont.
The newly-co-opted MLA paid tribute to her predecessor.
"I want to pay tribute to Seán Lynch for his years of tireless service to the people of Lisnaskea and Fermanagh and South Tyrone and also for the support and guidance he has given me," she said.
She said her priorities were delivering a better health service, building more homes and creating jobs.
"This is an exciting time in politics across our island and I look forward to playing my part as an MLA to build a better, fairer, greener new and united Ireland for all," Ms Murphy said.
