A family close to the couple confirmed that they have been separated since May.
Winstead also broke up with her husband in May.
Mary Elizabeth Winstead was seen sharing a passionate kiss with Ewan McGregor.
His three Emmy Award nominations including Outstanding Lead Actor in a Limited Series or Movie for this year's FX miniseries "Fargo", in which he played the dual roles of brothers Ray and Emmit Stussy.
McGregor, 46, met the attractive brunette at The Good Life Eatery in St John's Wood, North West London over the weekend. The couple have four children together.
The Trainspotting star has been married to production designer Mavrakis, 51, for 22 years since meeting on the set of British TV series Kavanagh QC.
As for the now-exes, they've been married since 1995. and have 4 daughters together. The cafe was really busy with people coming in and out the whole time. "As they left he got on to the back of Ewan's motorbike and they sped off together". A customer tells the tabloid the pair seemed "relaxed" together and were "deep in conversation" for more than an hour.
In February, Winstead shared a photo with McGregor on her Instagram with the caption, 'Pretty lovely Canadian Sunday. "I love you always, Riley", Winstead wrote, according to The Cut. "Sitting here with my best friend who I love with all my heart".