The Perfect Steak Marinade For Flat Iron Steaks

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This Flat Iron Steak Marinade comes together in five minutes, chills in the fridge, and transforms a flat iron steak into a tender, juicy dinner that rivals a $30 steakhouse dish, all without the extra oil.

You’ll love these steaks served with a Classic Wedge Salad and Loaded Baked Potatoes.

Below you’ll find step-by-step photos, grill tips, and all my favorite side-dish pairings.

Flat Iron Steaks on a cutting board after being in a marinade.

We used this marinade repeatedly in my meal-prep business, and it has been my go-to ever since. The three-minute mix works on chicken, pork, or steak, and after years of testing on grills, in ovens, and in skillets, it has proven to be truly foolproof.

Marinate for 30 minutes or up to 24 hours, and you will always end up with juicy, flavor-packed meat.

Tips for Grilling Steaks

Start hot. Heat your grill (or cast-iron skillet) to around 500 °F before the steak goes on.
Pat dry. Blot off excess marinade so the surface sears, not steams.
Season. Give each side a quick hit of kosher salt right before grilling.
Oil the grates, not the steak. Swipe a paper towel dipped in oil across the grates to prevent sticking.
Check temp. Pull at 130 °F for medium-rare (or your preferred number).
Rest 5–10 min. Let the juices settle, then slice against the grain and serve.

Flat Iron steaks in marinade in a glass bowl.

Ingredients and Substitutes

Ingredients to make a marinade for steaks including parsley, garlic, balsamic vinegar, diced onion, worcestershire sauce, soy sauce, flat iron steaks and brown sugar.

Recipe Notes

Protein – Works on any steak cut and pork tenderloin—pick what’s on sale or in the freezer.
Soy Sauce → Tamari – Tamari is your straight-swap if you need the marinade to be gluten-free.
Brown Sugar → Any Sweetener – Honey, maple syrup, or white sugar all replace brown sugar 1-for-1.
Onion & Garlic – These two carry most of the flavor. Use more, use less—just don’t skip both.
Fresh Parsley – Toss it in for a fresh pop of color; leave it out if you’re out.

If you remember only three things:

Swap tamari for soy to keep it gluten-free.
Any 1:1 sweetener will work.
The marinade is protein-agnostic—great on other steaks or pork tenderloin.

How to Make the Perfect Steak Marinade

Step 1: In a large bowl, whisk together soy sauce, balsamic vinegar, Worcestershire sauce, brown sugar, finely diced onion, minced garlic, and parsley.

Step 2: Into the same bowl place steaks into the marinade and cover with plastic wrap. You could also use a resealable plastic bag to store the steaks while they marinade.

Step 3: Marinate for 1 hour up to overnight.

Steak marinade in glass bowl with steaks on a cutting board and parsley in a white bowl.

Steaks in a bowl with marinade and plastic wrap over the top.

Step 4: Remove steaks from the marinade. Pat the steaks dry and sprinkle with kosher salt and black pepper before grilling. Discard marinade.

FAQ

Can I freeze the steak in the marinade?

Yes, you can freeze for up to 2 months; thaw overnight in the fridge, then grill as directed.

Is the marinade gluten-free?

Swap soy sauce for tamari and you’re good to go.

Can I cook the steak inside if I don’t have a grill?

Yes, you can cook inside with a cast-iron skillet or a grill pan. Sear in a smoking-hot cast-iron skillet, then finish in a 400 °F oven to your target temp.

How sweet is the finished steak?

The sugar simply aids in caramelization; the final steak is savory, not sweet.

What to Serve with Marinated Steaks

Creamy mashed potatoes with a side of roasted veggies is my go-to steak plate, but the leftovers are where the fun really starts.

Slice the meat thin and layer it over a crisp salad, stuff it into tacos or burritos, pile it on a toasted bun for a steak sandwich, or toss it with pasta for a quick weeknight bowl. It’s even perfect over rice and beans when you want something extra hearty. Pair any of these with a glass of your favorite wine and dinner’s done.

More Side Dish Suggestions

Did you make the recipe? Let us know what you thought by leaving a comment below and sharing it on Instagram, Pinterest, and Facebook! Thanks so much!

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