Former premier Dr Mahathir Mohamad will give a special lecture at the Pakatan Harapan's first ever convention this Saturday, said Harapan chief secretary Saifuddin Abdullah.

The convention is to discuss the formation of a grand opposition coalition to ensure straight fights with BN in the 14th general election, he said.

Mahathir, who was the longest-serving Umno president, is now Parti Pribumi Bersatu Malaysia (Bersatu) chairperson.

Bersatu president and ex-Umno number two Muhyiddin Yassin is also scheduled to speak at the convention, which will be attended by 1,000 delegates from PKR, DAP and Amanah.

He will speak alongside DAP secretary-general Lim Guan Eng, PKR president Dr Wan Azizah Wan Ismail and Amanah president Mohamad Sabu.

PAS was also invited to the convention but declined due to bad blood between the Islamist party and DAP.

There was no mention of Parti Warisan Sabah, the newly-formed party led by former Umno vice-president Mohd Shafie Apdal.