Lucy meets Tom in "The Master Plan" after he came to the bar to settle his tab from the night before when he unsuccessfully attempted to pick up several girls by buying drinks for them. Rather than try to pick up Lucy like the other girls, he simply acts like himself, and the two end up hitting it off and started dating. Lucy is intelligent and funny, and she freely accepts Tom's immature and sometimes inappropriate personality. She jokingly claims to be attracted to Tom because "You're cute and you're small enough for me to throw you around."
It eventually became clear to Lucy that Tom was not over his ex-wife Wendy Haverford, particularly due to how upset he got when Ron Swanson started dating her. In "Time Capsule", Lucy breaks up with Tom but tells him he should call her if he ever gets over Wendy.
In "End of the World", Lucy is going to graduate school in Bloomington. She attends Tom's final Entertainment 720 party before the company shuts down after Jean-Ralphio Saperstein calls her, telling her it was a special occasion and she should come down. Tom thinks Jean-Ralphio was trying to help him get back together with Lucy and thanks him, but Jean-Ralphio later tells the camera he forget Tom and Lucy ever dated and he was "trying to hit that". Lucy and Tom, however, have a good time and she kisses Tom the next morning, hinting at the possibility of their relationship starting up again.
In "Ron & Jammy", Tom goes to Chicago, where Lucy now lives, thinking there might be a chance to get back together with her. He ends up offering her Lucy a job managing Tom's Bistro, to which she replies that she needs to talk it over with her boyfriend first. The episode concludes with Lucy back in Pawnee, going over taxes, and joking around with Tom. Andy notes, "Tom & Lucy are totally going to fall in love". In "Gryzzlbox", she goes to visit her boyfriend Conrad in Chicago. When she comes back, she reveals to Tom that she and Conrad have broken up.
In "Save JJ's", Tom asks Lucy if she wanted to go to Donna's wedding with him. In a panic, he adds that they would only be going as colleagues and that she would supervise the catering. When he and Lucy see each other again, Tom reveals to her that he actually wanted to go as Lucy's date, to which Lucy happily agrees. In "Donna & Joe", they wear matching outfits to Donna and Joe's pre-wedding gathering and Tom tells Ron that he can picture spending the rest of his life with her, and that he would "marry her tomorrow". Ron tells Lucy this, which makes her feel uncomfortable. Tom explains himself to Lucy and she ends up forgiving him.
In "Two Funerals", Tom takes Lucy to the Snakehole Lounge, where they first met, and sets up a table with a vase filled with one single daisy explaining he had given her one single daisy in their previous relationship, and a stack of pancakes from JJ's Diner. He talks about their first date at JJ's, where they ate pancakes and Tom attempted (and failed) to show Lucy a card trick he'd learned. He takes out a deck of cards and tries the trick again. When Lucy looks at her card, it says "Will you marry me?", to which she says yes.