The duo sparked speculation they're engaged when the actress showed off a diamond ring on her wedding finger, reported Female First.
The 31-year-old actress posted a selfie onto her Instagram account as she got ready to attend a wedding but fans were quick to spot the sparkler on her left hand.
One said, "Look at that big ring on her wedding finger", while another said, "That definitely looks like an engagement ring, I hope it is!"
Martin, 39, and Wallis apparently started dating in March and are said to be smitten with each other.
The speculation comes just days after Martin and Paltrow's divorce was officially announced.