McGann was born in Kensington, Liverpool, Merseyside, and began his professional acting career in 1982, starring in the West End musical Yakety Yak. He has since worked extensively in British theatre and on screen.
In 1989, he starred as Mickey in the West End hit musical Blood Brothers. In 1990, he played Johann Strauss in the international mini-series, The Strauss Dynasty. In 1993, he created, co-produced and starred in the award-winning BBC drama The Hanging Gale. He portrayed the character of Sean Reynolds in Emmerdale from 1999 to 2002.
In 2003, he starred with Jamie Theakston in the hit West End play 'Art'. In 2006, he played the role of the Reverend Shaw in the original West End cast of the musical Footloose. He can currently be seen playing Dr. Turner in BBC TV series Call the Midwife.
He was a guest speaker at the Cambridge Science Festival in March 2015. He published a guest essay in the Journal of the Royal Society of Medicine in April 2015, discussing issues of medical accuracy and communication in Call the Midwife.
In July 2017, McGann published "Flesh and Blood: A History of My Family in Seven Maladies" - a personal history of his family over a century and a half as told through the medical ailments they suffered.
