The Split and Unforgotten star Walker appears opposite Sean Bean in the BBC One series about a long-married couple facing new challenges and revealed the scene that stuck in her mind from filming.
She said: "My most memorable scene was applying cream to Sean Bean’s thigh area. It was a beautiful moment and one that I never expected, as Ian had a nasty rash.
"It was a tremendous day in my professional career. Luckily it was in a tasteful position for camera."
Game Of Thrones star Bean has recently come under fire for his comments on intimacy coordinators, used on film and TV sets to support actors playing sex scenes.
The rise in employing intimacy coordinators in shows such as Normal People has been hailed as a great development by many actors, but Bean claimed that it "spoils the spontaneity" of the moment - leading Emma Thompson, Rachel Zegler and Jameela Jamil to speak out against him.
He also said: "It would inhibit me more because it's drawing attention to things. Somebody saying, ‘Do this, put your hand there, while you touch his thing...' I think the natural way lovers behave would be ruined by someone bringing it right down to a technical exercise."
However, Walker had no complaints about playing Bean's wife in Marriage, saying: "It’s been very easy being married to Sean Bean for 27 years on this."
Bean seemed equally keen on his co-star as he added: "It’s been a real pleasure for me working with Nicola, and I know everyone says that, but it really has."
The series also stars Henry Lloyd-Hughes as Walker's character's colleague and Chantelle Alle as the couple's daughter.
Marriage begins on Sunday at 9pm on BBC One.
Watch: Emma Thompson responds to Sean Bean's criticism of intimacy coordinators