The filmmaker, 44, and the actor, 21, who met on the set of 2009 biopic Nowhere Boy, have welcomed a second daughter into their family, reports Britain's Daily Mail.
Taylor-Wood gave birth to the couple's first child, Wylda Rae, in July 2010.
The arrival of the tot comes a month after the heavily pregnant artist collected an Order of the British Empire (OBE) medal from Charles, Prince of Wales, in December (11).
The baby is Taylor Wood's fourth daughter - she has two girls, Anjelica, 14, and Jessie, five - from her previous marriage to art dealer Jay Jopling.
Taylor-Wood and Johnson became engaged in 2009.