And fans were impressed with the BBC show, describing it as “brilliant” and “gripping”.
The six-part series achieved an audience share of 35 per cent, the BBC said, with an average overnight rating of 6.7 million for Sunday’s opening episode.
Game Of Thrones star Richard Madden, who plays bodyguard David Budd, said: “I was fascinated with David being a series of different characters.
“He has a sense of duty and also a political history because he’s a former soldier who’s been in Afghanistan and Iraq.
“David’s a man adjusting to civilian life and dealing with some of his own mental health issues.”
Other notable cast members include Line Of Duty star Gina McKee as Anne Sampson and Peaky Blinders favourite Sophie Rundle as Vicky Budd.
Former Labour Home Secretary Jacqui Smith said she believed the script was true to life.
But some government ministers believe the storyline is too far-fetched to take place.
Writer Jed Mercurio defended the plot and added: “Well, you’ve got two very attractive people in a high-pressured situation.”
Many viewers took to social media to say they were gripped by the thriller.
“Opening 20 minutes most tense drama this year,” one wrote.
“Richard Madden is immense and Keeley Hawes is as excellent as ever.”
Another posted: “Bodyguard was brilliant!! Literally on the edge of my seat!!”
Episode two aired last night.
The remaining episodes will be aired on BBC One on Sundays.