The couple, who Wednesday in 2011, already have a four-year-old daughter, Mia.
When Kate Middleton and Prince William welcomed their third child Prince Louis on 23 April, he weighed in at 8lbs 7oz, making him 12oz lighter than the new royal addition to Zara and Mike Tindall's family. The palace said the baby weighs nine pounds three ounces (4.2 kilograms).
The couple's choice of baby name has not yet been revealed but the palace confirms it will be "in due course".More news: Incredibles 2 makes heroic North America box office debut
"This baby is the second child for Zara and Mike, the fourth grandchild for The Princess Royal and the seventh great-grandchild for The Queen and The Duke of Edinburgh". Mr Tindall was present at the birth.
The Queen is said to be "delighted" by news of her seventh great-grandchild.
Zara, the Queen's granddaughter, gave birth to the baby girl, weighing 9lb 3oz, at Stroud Maternity Unit in Gloucestershire on Monday.More news: Figures Show About 2000 Minors Separated From Families At US Border
The happy announcement comes more than a year after the couple faced heartbreak when Zara suffered a miscarriage just before Christmas in 2016.
"Very sadly, Zara and Mike Tindall have lost their baby", Tindall's spokesperson told People in a statement at the time.
Zara, 37, won an equestrian silver at the London Olympic Games in 2012 while her 39-year-old husband was part of the England team that won the rugby World Cup in 2003.More news: OxygenOS 5.1.7 update for the OnePlus 6 fixes bootloader vulnerability
When Zara - daughter of the Princess Royal - was born in 1981, she had no right to a title, being born down the female line as the offspring of a daughter of a sovereign.