Her candidacy was announced by Chief Minister and state Barisan chairman Datuk Amar Abang Johari Tun Openg at PBB headquarters here Wednesday.
"I have indicated it to her and she has indicated her willingness to be the candidate," he said, adding that Barisan chairman Datuk Seri Najib Tun Razak had also agreed to it.
Abang Johari said Jamilah, 62, is the most suitable choice as she had been by Adenan's side throughout his years as an assemblyman, first in Muara Tuang and then in Tanjong Datu.
"She has been very active and gone to the ground to help Tok Nan. I can tell you that she is really a grassroots leader," he said.
Jamilah was not present at the announcement.
The Tanjong Datu state seat fell vacant when Adenan died from heart complications on Jan 11.
In last May's state election, Adenan retained the seat with a 5,892-vote majority, defeating PKR's Jazolkipli Numan who only got 468 votes.
Nomination for the by-election is on Saturday while polling has been fixed on Feb 18.