The 34-year-old actor and cartoonist — best known for playing Gryffindor student and Ron Weasley's love interest Lavender Brown in the hit wizarding movie franchise — announced the birth of her new baby on Instagram.
Cave shared pictures of the new arrival, along with an image of the Brazilian soccer player, captioned: "Welcome Becker Brown. Thank you to UCLH. Thank you to the midwives Amy and Emi-Lou. Thank you to Alisson Becker."
The gender of the new baby has not been confirmed.
Cave and her partner, comedian Alfie Brown, are also parents to five-year-old daughter Margot and sons Donnie, seven, and 17-month-old Tennessee.
The writer and comedian was treated in hospital earlier this month after she contracted coronavirus.
She shared on social media: "Triage, once again…… Anyone else had COVID in 3rd trimester & had it hit them like a tonne of bricks for weeks?"
The Harry Potter star's son Tennessee was born during the coronavirus pandemic and spent several days on the neonatal unit after a difficult labour.
He then returned to hospital as a newborn after he tested positive for COVID-19.
Cave said her son seemed "completely fine" before things "suddenly turned" when he contracted the virus.
“That’s the thing about newborns, you have to be so hyper aware of every symptom and just to trust your instincts.
“Within a day of realising he was just kind of changing a little bit, he wasn’t feeding as much and his cry was different, it was like a different baby. I just went for it and I went into A&E. I think that’s what everyone has to do."
Cave has previously spoken about the unconventional start to her relationship with Brown, as she fell pregnant with their first child in what was a one night stand.
The couple split shortly after their daughter’s birth, but rekindled their relationship after a few years apart.
As well as her work as a cartoonist, Cave has continued acting and has appeared in programmes such as Trollied and Buffering as well as 2014 film Pride.
Brown, whose mother is impressionist Jan Ravens, has been touring with his stand-up comedy show Sensitive Man.
Watch: Jessie Cave's third child contracted COVID as a newborn