The BBC One drama follows three very different families, and the show's central characters are based on women whom Hughes interviewed (all names have been changed to protect their anonymity and privacy).
The series synopsis reads, "A mother faces prison for trying to help her pregnant teenage daughter. Two young newlyweds learn that their much-wanted first child will die of a fatal foetal abnormality. If they lived in England, Wales or Scotland, both families could seek a legal termination. But this is Northern Ireland, where abortion laws have been among the most restrictive in Europe."
Read on for everything you need to know about the cast and characters in Three Families.
Sinéad Keenan plays Theresa
Who is Theresa? A religious mother of two whose teenage daughter falls pregnant, and whose experience is based on a real-life court case.
Speaking about the real-life "Theresa" (not her real name), screenwriter Gwyneth Hughes said, "The real 'Theresa' chose her daughter over the traditions of her faith, and had to find reserves of courage and endurance which almost broke her."
She also stated, "Classically the abortion debate is presented as two opposing and immoveable camps – 'pro Life', and 'pro Choice'. But as I discovered, it’s not as simple as that. What about people like our character Theresa, who thought she was against abortion until her own 15-year-old daughter fell pregnant?"
Where have you seen Sinéad Keenan before? The actress is known for Deep Water, Being Human, Little Boy Blue, Married to a Paedophile, and Porters, among other projects.
Amy James-Kelly plays Hannah
Who is Hannah? A young married woman who longs for a child, but whose much-wanted first pregnancy ends in tragedy.
"The real 'Hannah' is a spirited, funny, vivid young married woman from a small town; I loved her positive attitude and the joy she managed to retrieve from her terrible ordeal," Gwyneth Hughes said.
Where have you seen Amy James-Kelly before? She recently played Suzannah Washington in BBC One period drama Gentleman Jack, and is also known for roles in Military Wives, The Bay, Safe, and Jericho. She played Maddie Heath in Coronation Street.
Genevieve O’Reilly plays Rosie
Who is Rosie? An affluent married woman with a history of mental health issues.
Hughes said, "The real 'Rosie' is a warm, beautiful, elegant older woman, who thought the chance of a baby had passed her by, and whose mental and physical suffering was extreme."
Where have you seen Genevieve O'Reilly before? International viewers will recognise O'Reilly for her work in the Star Wars franchise as Mon Mothma, portraying the character in Star Wars: Revenge of the Sith and Rogue One. Other projects have included The Matrix Reloaded, Glitch, Banished, and Tin Star (as Angela Worth).
Lola Petticrew plays Orla
Who is Orla? A 15-year-old schoolgirl who seeks to terminate her unwanted pregnancy with the help of her mother, Theresa.
Where have you seen Lola Petticrew before? She played Izzy Brannick in Bloodlands, and will star in the upcoming Channel 5 historical thriller Anne Boleyn in the role of Jane Seymour.
Colin Morgan plays Jonathan
Who is Jonathan? Hannah's supportive husband.
Where have you seen Colin Morgan before? He's best known for playing the title role in the TV fantasy series Merlin, and as Leo Elster in Humans seasons one-three. He also starred in Testament of Youth, Legend, Netflix royal biopic The Crown, and The Fall.
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Prasanna Puwanarajah plays David
Who is David? Rosie's husband, who (unlike his wife) is not from Northern Ireland.
Where have you seen Prasanna Puwanarajah? He recently played Ashley in Defending the Guilty, and is known for roles in Doctor Foster (James), Critical, Mum, and Patrick Melrose (as Johnny).
Owen McDonnell plays Mark
Who is Mark? Theresa's partner, and step-father to teenager Orla.
Where have you seen Owen McDonnel before? He's best known for playing Eve's husband Niko Polastri in the BBC series Killing Eve. Other projects have included Paula, Responsible Child, The Bay, Women on the Verge, and Dominion Creek.
Kerri Quinn plays Louise
Who is Louise? Theresa's best friend; she's staunchly pro-life and has very different views on abortion to her friend.
"The character Louise gripped me from the get go and I was intrigued to know more about her motivation for being so proactive. There are three stories told in this drama but in my head there were four when you consider Louise’s struggle with the abortion laws. There is a beautiful honesty with Louise," Kerri Quinn said.
Where have you seen Kerri Quinn before? She played Rita in Derry Girls and Vicky Jefferies in Coronation Street, among other series.