He will also lead and organise the scrutiny of the government's positions and actions in Parliament, and be consulted on the appointment of opposition members to Select Committees, such as the Public Accounts Committee.
Singh, who is also a lawyer, will receive an annual package of 385,000 Singapore dollars ($2,79,025.98) as allowances for his new role.
Prime Minister Lee said on July 11 that Singh will be designated the Leader of the Opposition.
After his swearing-in on Monday, Lee said that the election results have shown a strong desire among Singaporeans for a greater diversity of views in politics and that the trend is here to stay.