Twenty-six-year-old Tareena Shakil is thought to have become the first UK national to be convicted after returning home. She took her baby son to Raqqa, the "Islamic State" (IS) terror group's de facto capital.
Shakil denied charges that she had traveled to Syria to support Islamic State (IS), or posted messages encouraging terrorism on Twitter before she left.
A court in Birmingham, central England, heard how she had been radicalized on the Internet.
The jury were shown tweets, messages and photos, which prosecutors said proved she was a member of IS. Some of the her messages called on people to "take up arms," the UK's Press Association reported.
Shakil told her family in October 2014 she was going for a beach holiday in Turkey. But instead, she crossed the border with her son into Syria and headed to the IS stronghold of Raqqa, before later returning home claiming she'd "made a mistake."
In Syria, Shakil and her son were kept in a large house with other single women. During their stay, she posed with the toddler for a selfie while wearing a black balaclava branded with the IS symbol.
Lasted three months
She later complained that life under IS was too strict and repeatedly looked up the phrase "I want to leave ISIS" (another acronym for the jihadist group) on the Internet.
Shakil told the court that after deciding to escape, the pair rushed back to the Turkish border by road, avoided a three-man IS patrol on the way, and then turned themselves in to the Turkish military.
Last February, police boarded her flight home at London's Heathrow Airport to arrest her.
In her defense, the 26-year-old said she only traveled to Syria because she wanted to live under sharia law.
Concerns for son
British children's charities have denounced how Shakil put her young son at substantial risk of death by taking him to Raqqa in the middle of a civil war. He has not been identified and his whereabouts is unknown.
Shakil, who is believed to be one of about 60 women who have traveled to Syria to join IS, will be sentenced on Monday.