Whenever you follow classic software or product development process then you have two primary roles needing to be filled by strong, smart people. Most people have heard of the project manager. That person is responsible for coordinating resources (people) and processes to deliver products on time and on budget. But the biggest measure of project success hands down is if the new product adds value to its business. There is a set of metrics used to judge business success and they are business requirements. You can read the article on that topic here. You need a business owner tick, and the project manager tock - for your project clock to tick along.
A business manager, non-technical, needs to be part of a group of business people who creates the lists of business needs that must be satisfied in order to claim the project is successful. This ultimately is the criteria that determines the functional success of the project. One person, a business manager, needs to be the "business owner" for the project. So there is no confusion, it doesn't have to be the actual owner of a business.
The business owner of the project needs to be the person the project manager is beholden to. The business owner needs to have regular meetings with the project manager and make sure the project is meeting time and cost schedules. The business owner also has the responsibility of clearing business barriers inside the company. Barriers can be unpaid bills, uncooperative business managers, poorly defined business processes and just about any non-technical thing you can think of. Ultimately, the business owner will judge the project deliverables and declare whether or not the
You MUST have a business owner involved in the projects. It's absolutely necessary for success.