The candidates are (BN) Suhami Sabudin, 44, (PKR) Datuk Seri Dr Wan Azizah Wan Ismail, 62, (PRM) Azman Shah, 50, and Independent Salleh Isahak, 53.
All the candidates had submitted their nomination papers at the Dewan Perdana Institut Kemahiran Belia Negara, Bukit Mertajam by 10am.
Independent candidate, Salleh is also a member of UMNO Alma branch, arrived at 8.40am followed by Suhaimi at 8.45am.
Dr Wan Azizah arrived at 8.50am while Azman came just before 10am.
READ: Dr Wan Azizah to contest Permatang Pauh again
Also present to lend support were UMNO deputy president Tan Sri Muhyiddin Yassin, UMNO vice-president Datuk Seri Dr Ahmad Zahid Hamidi, UMNO Information chief Datuk Ahmad Maslan, MIC president Datuk Seri G. Palanivel and Gerakan president Datuk Mah Siew Keong.
Dr Wan Azizah was accompanied by her daughters Nurul Izzah Anwar and Nurul Nuha Anwar, PKR deputy president Azmin Ali, DAP secretary-general Lim Guan Eng and PAS deputy president Mohamad Sabu.
The Election Commission (EC) had set polling date for the by-election on May 7, while early voting is set on May 3.
According to the EC, there are 71,820 registered voters in Permatang Pauh with 627 early voters.
The Permatang Pauh seat fell vacant after Datuk Seri Anwar Ibrahim, who is serving a five-year jail sentence for sodomy, was disqualified as a Member of Parliament on March 16 when a petition for a royal pardon by Anwar's family over his conviction for sodomising his former aide Mohd Saiful Bukhari Azlan was rejected by the Pardons Board.
READ ALSO: Royal pardon rejected, Anwar disqualified as MP
The Permatang Pauh parliamentary seat is seen as PKR’s strong fort when it won the seat since 1982.
Anwar was the MP in 1982, 1986, 1990 and 1995 before being jailed for six years in 1999 for being found guilty of four corruption charges for misuse of power.
His wife, Dr Wan Azizah later took over as MP in 1999 until 2008 before vacating the seat to provide path for Anwar following his release in 2004.
ALSO READ: PKR, is there really nobody else?
This is the 10th by-election to be held in the country after the 13th general election which was held on May 5, 2013.