Megan Mullally and Nick Offerman's 21-year marriage is rare in Hollywood. They have a piece of advice.

Megan Mullally and Nick Offerman share a marriage and partnership forged in creativity.

You likely know them best for their scene-stealing roles as Karen Walker in Will & Grace and Ron Swanson in Parks and Recreation. But in the 20-odd years they've been together, they've also co-authored The New York Times bestselling memoir The Greatest Love Story Ever Told, co-hosted the podcast In Bed With Nick and Megan and starred in countless films and TV series.

A 21-year marriage like theirs feels rare in Hollywood, where celebrity splits are easier to rattle off than long-lasting couples.

Offerman and Mullally met in 2000, when they starred in the play The Berlin Circle. They got engaged in London two years later and married in a surprise wedding at their Los Angeles home in September 2003, on the night before the Emmys.

First, listen to Nick Offerman and Megan Mullally on No Filter. Post continues below.

Their 'big secret' to a successful marriage is much simpler than you'd first guess.

"We've always liked each other," Mullally told Mamamia's No Filter podcast. "I know that sounds kind of obvious, but I'm not sure that every married couple does.

"I think we've been really lucky — we're both very romantic, but we're also really good friends."

In fact, the couple says their relationship has never been stronger.

"Recently, we looked at each other within the last six months or so, and decided that we thought our relationship was better now than it's ever been," Mullally said.

It could be easy to attribute that to having been together for 25 years, but a lot of it boils down to communication.

"As good listeners, we understand the simple truth that if you make a promise to a person that you're going to spend the rest of your lives together, you can either make it difficult, or when things do get difficult … we can say, 'Okay, I still want to live in this house with you tomorrow, so I can either compromise and find a resolution here'," Offerman said.

"I think we just have the wherewithal to be open and keep growing."

Megan Mullally. Image: Ramona Rosales/ Vivid Sydney

Their glowing adoration for each other is evident in how they talk about one another.

"Early on, when I met Megan and began living with her and saw her work in her various different mediums, what struck me the most about her was her incredible work ethic," Offerman said.

"If you were given the gifts that she was born with, I would assume I'd rest easy on my laurels and just let people feed me caviar all day. But Megan works harder than anyone I've ever seen."

Over the years, they've collaborated on so many projects together. Currently, they're bringing their live show, Unscripted & Unfiltered, to Vivid Sydney in June.

But when love and work overlap so often for these creatives, one can't help but wonder where they draw the line and if they ever truly switch off.

They know they are lucky to have flexible, creative jobs that allow for some breathing room.

"It's not like we're both working at Wall Street or something, where we just have a daily consistent grind, and we're like, 'You drop the kids off the pool'," Offerman mused.

They take turns being away: one works for a month, then they switch. They don't have kids (only dogs) which makes it easier, too.

"We do a good job of just kind of handing off and passing the baton back and forth," Offerman said.

"Sometimes, when we do something together and collaborate on a show, to be a little more conscientious — because we're working on it at home in our living space — when do we clock out, say, 'Okay, let's change our hats and just watch some TV'."

Nick Offerman. Image: Joe Carrotta.

After all these years — through stage productions, memoirs, and podcasts — their bond is unmistakable. But for so many of us, they'll always be Karen Walker and Ron Swanson first.

So, how do Mullally and Offerman feel about the characters that made them iconic? And as time passes, do they ever pause to celebrate the legacy those roles have created?

"I'm grateful to have been able to play that role. And it was such a fun part to play and so well written," Mullally said.

As her career progressed, Mullally discovered her true passion lies in music.

"I have a band called Nancy and Beth that I love," she said. Plus, there's the interior design company she's starting with her friend and another long-term podcast project on the way.

As for Offerman? He'll always be grateful for good ol' Ron.

"It took me from obscurity to putting me sort of on the map, and led to so many other opportunities, from acting roles to writing books and touring as a humorist and so there are much worse problems to have than to be like associated with one huge overarching role," he reflected.

"Getting a job as an actor is like winning the lottery. So getting one that resonates with people, and that, that I would watch and be entertained by myself is, winning the triple lottery or something," he said. "So I would be happy to shake Ron's hand and serve him a steak if he showed up."

Feature image: Emily Shur/ Getty.