Byworth has been promoted to the role after a six-month stint as acting chief executive.
The change follows Charles Badenoch's move to another position in the charity. Badenoch, who headed the charity's UK office for five-and-a-half years, is now international vice president for global advocacy and justice for children. Since joining the charity as a graduate trainee in 1988, Byworth has worked for World Vision in the UK, Asia and Africa. He said the organisation was "uniquely positioned to be the most engaging way for the British public to make a real and lasting difference to the lives of children facing poverty and injustice in some of world's poorest places".