The singer, 39, posted a picture of the new arrival on Instagram with her husband, The Feeling bassist Richard Jones.
She wrote: “He’s here! Mickey Jones born today weighing 7lb 1oz and he’s absolutely gorgeous.
The Read My Lips star has been inundated with congratulatory messages from her followers on the app and the photo she shared, which shows Jones cradling the newborn, has amassed more than 12,400 likes.
Her older children – all shared with her husband – are Sonny, 14; Kit, nine; six-year-old Ray and two-year-old Jesse.
Mickey is likely to be the last of the bunch, with Ellis-Bextor having recently said she would “probably call it a day” after having child number five.