[2] Lenehan made her screen debut appearing in the 1979 made-for-television movie When She Was Bad... starring Cheryl Ladd and later guest-starred on Alice.

She made her big screen debut in the 1980 action comedy film Smokey and the Bandit II playing the supporting role.

On television, Lenehan guest-starred on both comedy and dramas including Hill Street Blues, Family Ties, The Facts of Life, Fame, The Twilight Zone, Beauty and the Beast, The Tracey Ullman Show, Murphy Brown, Roseanne, The Golden Girls and Seinfeld.

She also had a recurring role on the ABC sitcom Ellen during its fourth season, playing the title character's realtor, Margaret Reed.

Lenehan has appeared in featured, recurring and guest roles in more than 100 television shows, including Malcolm in the Middle, Everybody Loves Raymond, How I Met Your Mother, Judging Amy, Gilmore Girls, Caroline in the City (playing office manager Plum in two episodes in Season 4), Dharma & Greg, Buffy the Vampire Slayer, 3rd Rock from the Sun, ER, Boy Meets World, The Nanny, Quantum Leap, Just Shoot Me!, Ally McBeal, That '70s Show, Nip/Tuck, The New Adventures of Old Christine, The Middle, Black-ish, Superstore, Bless This Mess and Grace and Frankie.