The 50-year-old Workers' Party executive council member said this in a note posted on his Facebook fan page on Friday morning.
"It is quite clear to me that given my new responsibilities as MP I will not be able to continue practicing law the way I have in the last twenty years," he wrote, adding that leaving the firm will give him more time for his family, constituency and country, and "to explore alternative work arrangements".
"Law is in my blood and no doubt it will be part of my life," he added, thanking his partners, colleagues and clients for the experiences he has received over the years practicing with the firm.
Netizens applauded his decision, with Chen's note receiving over 400 likes and more than 100 comments since it was first posted.
User Er Han Koon commented, "Thank you, Mr Chen, for showing us what true sacrifice and honour means."
Shirryn Quek, also wrote, "I salute you for your courage and dedication to Singaporeans. Aljunied residents are so fortunate to have you as their MP."