The woman - a 45-year-old mother of two - was convicted in August along with an unmarried Sri Lankan man.
She was sentenced to death by stoning, while the man was sentenced to 100 lashes.
Saudi Arabia's decision to stone the woman was condemned in Sri Lanka, where protests were held.
Sri Lankan embassy officials visited the woman in a Saudi jail on Sunday, Deputy Foreign Minister Harsha de Silva said.
The country had appealed to Saudi Arabia's government to pardon the couple.
"Through our intervention, they have agreed to reopen the case," Mr de Silva said.
"This is a big victory. We will provide her with legal help."
Deputy minister Ranjan Ramanayake added that the Sri Lankan government was informed about the woman's case only after she had been convicted in August 2015 - despite the fact she was arrested in April 2014.
"Islamic Sharia law says four respected Muslims need to be eyewitnesses for this type of case, but this has not been possible in this case," he said.
"Unfortunately, not knowing the law, she has confessed under pressure without any legal help."
Protests were held outside the UN compound and the Saudi embassy in Sri Lanka's capital, Colombo - with some calling for a ban on sending Sri Lankan workers to Saudi Arabia.
The Sri Lankan government says it is gradually reducing the number of women sent to work in the Middle East.
Saudi Arabia has agreed to reopen the case of a Sri Lankan maid sentenced to death for adultery, Sri Lanka's deputy foreign minister said.