Seri Setia assemblyperson Shaharuddin Badaruddin has died following a protracted battle with colon cancer.
According to his aide Zafrullah Aris, the PKR vice-president, aged 56, breathed his last at 6.28pm at the Putrajaya Hospital.
"His remains will be taken to his house in Desa Pinggiran Putra and the burial will take place tomorrow," he said in a statement.
In a Twitter post, Selangor Menteri Besar Amirudin Shari said Shaharuddin's death was a great loss for the state.
"I have received the sad news that my friend has passed away. May Allah shower blessings upon his soul," he added.
In the May 9 general election, Shahruddin, who is also a Selangor state executive councillor, won the Seri Setia seat by a landslide garnering 29,250 votes.
He defeated BN's Yusoff M Haniff, PAS' Mohd Ghazali Daud and independent S Vigneswaran.
Shaharuddin's death paves the way for the third by-election in Selangor since the general election.
Shaharuddin has been a lifelong academic, serving 30 years at Universiti Teknologi Mara and later University of Selangor (Unisel) where he taught political science.
In 1998, when Shaharuddin was the secretary-general of the Muslim Youth Movement of Malaysia (Abim), he was among those arrested under the Internal Security Act 1960 (ISA) for his part in the reformasi movement.
The May 9 election was Shaharuddin's first electoral outing.