The acclaimed writer announced the endorsement on Tuesday in a Facebook message to Mr Obi on his birthday.

She described the politician as "my dearest Big Bro" and spoke glowingly on Mr Obi's "hope and belief in what Nigeria could be".

"Mummy called you her ‘first son,’ my siblings and I call you our 'big bro,' and I cannot wait to call you ‘My President'," she wrote.

"I cannot wait for February 25, 2023, when I, with personal pride in you and with hope for what Nigeria can become, will cast my vote for you and your running mate, Senator Yusuf Datti Baba-Ahmed."

https://www.facebook.com/chimamandaadichie/posts/pfbid02JpL1LeLDBh7ShzVihkVisX9Pwahsk95XeHM3pUnNnDpCPGukkFLfCdJYzZg7uisPl?__cft__[0]=AZVVKRtC4_RZ8hFDuXBcvKe2J6argzDK7zmAfIfvtzRpiKZPPTr7W2De6qi_J_YumAvaVXhz93T5EA87K7ABTLXT92v4Gvwcdo1tYLI346bgErO70ASlJAaeMup0aC_hJgNW9bx2c1VxyuI6GyLG20AeWTCPQH0T5APVRIhAtHxJyg&__tn__=%2CO%2CP-R

Mr Obi is a former governor of Anambra state with a reputation for frugality and sound management.

Other key contenders in the race include the ruling All Progressive Congress' (APC) Bola Tinubu and the People's Democratic Party's (PDP) Atiku Abubakar.