Congratulating the new parliament on its election, Rehman sent in her resignation to the caretaker Prime Minister Mir Hazar Khan Khoso, Pakistan Embassy spokesman Nadeem Hotiana said in a message posted on Twitter.
Another message on Twitter quoted Rehman as saying: "It is time a new envoy comes in as quickly as possible so that there is no gap in the relationship."
Rehman, 52, a close aide of Pakistan President Asif Ali Zardari, was appointed to the post by the PPP-led government in 2011.
A senior leader of the PPP and a former aide to slain party chief Benazir Bhutto, Rehman had also served as Information Minister in the PPP-led government.
Several other envoys appointed by the outgoing government are expected to quit following the PML-N's victory in the May 11 polls, which marked the first democratic transition of power in Pakistan's history.