The government hospital said it dismissed patient coordinator Roy Ngerng because his blogging activities criticising Prime Minister Lee Hsien Loong were "incompatible with the values and standards" it expects of its employees.
Ngerng made headlines recently for becoming the first blogger in Singapore to be sued over comments made online about a politician.
He is alleged to have written on his blog that Lee's government was mishandling state pension funds.
Court proceedings are expected to begin next month.
On his Facebook page, Ngerng said he expected to be fired.
"My supervisors have been patient but they also have a responsibility to uphold and I respect that," he wrote.
International human rights groups have criticized Singapore government officials for using threats of defamation suits as a way to silence opposition politicians and other dissenters in the tightly controlled Southeast Asian city-state.