At a press conference, she announced Lai, 57, would replace Lin Chuan who resigned on Monday, Efe news agency reported.
Lin's resignation came as Tsai's popularity has dropped below 30 per cent, down from 70 per cent when she took office in May 2016.
A strained relationship with Beijing, unpopular pension and labour reforms, and a huge power outage last month that left thousands across the country without electricity had increased the pressure on Tsai to replace Lin.
Lai, a doctor from the southern city of Tainan, started his political career in the 1990s, when he won a seat in the then National Assembly, followed by seats in the Parliament in 2001, 2004 and 2008.
He has been Mayor of Tainan, a stronghold of the reigning Democratic Progressive Party, since 2010.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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