After years of playing bit parts in U.S. TV programmes The Drew Carey Show and Law and Order, Walsh was chosen to play surgeon Addison Montgomery on hit medical series Grey's Anatomy at the age of 36.
And now the actress has encouraged young stars not to give up in the face of failure because determination always pays off.
In an article for Harper's Bazaar magazine, she writes, "Age is just a number. Unless, that is you live in Hollywood, where there's the notion that if you haven't hit it big by your 20s, you may as well hit the road. But if anyone told me that I would be thankful when I looked back on celebrating my 28th birthday alone in New York City with a piece of stale cheesecake, working at one of my three waitressing jobs, I would have punched him.
"During those broke years, I shared not one but two studio apartments, first with my brother, and then with my pal Karen, sleeping head to foot in the same bed. I never dreamed that one day I would land my breakout role at the ripe old age of 36."
And Walsh, who later received her own spin-off, Private Practice, is actually relieved she didn't make it big until her later years, insisting, "I had been able to actually live life, unobserved, paparazzi-free, and make a ton of mistakes in private."