The Short Answer
There is essentially no connection between Omni Hotels & Resorts and Marriott International. They are completely separate companies operating independently of one another. This confusion comes up frequently enough that I decided to just write out what actually exists between these two brands, because people ask about this in forums all the time. Omni is a privately held company founded in 1947 by Jack Ingram in San Antonio, Texas. They own and operate around 56 properties across North America and the Caribbean under brands like Omni, Granada, and Willard InterContinental. The current CEO is Mark Gold, who took over after Ingram's family sold a majority stake to a private equity firm called Blackstone in 2016. Marriott, on the other hand, is the largest hotel company in the world by a significant margin, with over 30 brands and 8,000+ properties globally. They have their own loyalty program called Marriott Bonvoy with 200+ million members. These two companies do not share ownership, they do not have a loyalty partnership, and you cannot earn or redeem points between their programs. Omni has its own loyalty program called Omni Select Guest, which gives members room upgrades, dining discounts, and occasional promotional offers. It operates completely independently from Bonvoy.
What people sometimes mistake for a connection is that both companies participate in the same major global distribution systems and online travel agencies. If you search for an Omni property on Expedia or Booking.com, you will see it right alongside Marriott properties. That surface-level coexistence on travel sites is about as far as any operational overlap goes. I ran into a specific issue last year when a client was trying to book a Marriott Bonvoy elite night credit strategy. They wanted to stay at an Omni property to count toward Marriott status, assuming there might be some kind of partnership I hadn't heard about. I had to tell them it would not work. Omni nights do not count toward Marriott Bonvoy status or tier qualification in any capacity. They checked three different loyalty program pages before they accepted it, and I still had to walk them through it. Here is something most people miss though. While there is no formal loyalty partnership, both Omni and Marriott are members of different but overlapping corporate negotiated rate programs. If your company has agreements with both hotels, you might be able to access corporate discount rates at properties from either brand through your employer's travel portal. That is not a partnership between the two hotel companies, it is just a feature of how corporate rate distribution works through platforms like Cvent or Concur. It creates the illusion of a connection where there isn't one.
There is also the matter of group and convention business. I have worked with meeting planners who try to negotiate blended rates across multiple hotel brands for large events. You can absolutely do this with Omni and Marriott simultaneously since they are both willing to discuss group contracts. Some cities even have both brands in the same downtown corridor, which makes itlogistically convenient for event organizers. But again, this is just normal competitive market dynamics, not any kind of formal alliance. If you are trying to maximize loyalty points and these are your only two options, here is what I would suggest. If you are already a Bonvoy member with elite status, stick with Marriott properties. The earned value of Bonvoy points, elite benefits, and room credits usually outweighs whatever Omni might offer. Omni Select Guest does provide decent perks like free parking at some locations and dining discounts, but those benefits do not transfer to Bonvoy or accumulate toward anything Marriott-related. The only scenario where I would actively recommend choosing Omni over Marriott is when the rate difference is substantial enough to justify it. I found this out the hard way during a trip to Austin where the Omni Barton Creek was pricing at nearly double what a nearby Marriott Autograph Collection property was going for. The Marriott was cheaper, but Omni included valet parking and a resort-style pool complex that the Marriott simply did not have. I stayed at the Omni and calculated that factoring in the $45 daily parking fee at the Marriott location, the total cost came out roughly equal. Worth knowing when you are making a decision.
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Bottom line, if someone tells you there is a partnership between Omni and Marriott, they are either mistaken or referring to something extremely niche that would not affect your booking in any practical way. These are two separate competitors in the upper upscale to luxury hotel segment, and treating them as connected will just lead to confusion about loyalty status, point earning, and benefit eligibility.