There are important differences between project and product management as well as commonalities.

The project manager:
The project manager is responsible for managing the assigned project in time and in budget.  Whether or not the project manager is eventually accountable for the deliverables depends on the project organization and governance the project is set up in.
The project cycle usually ends with acceptance and sign off of the deliverables as well as the formal project closure sign-off.

The product manager:
First of all a product manager is accountable for the respective product for the comlete product life cycle.  This cycle usually outlasts a typical project life cycle.  For example, a project life cycle may end with the delivery of a finished product whereas the product life cylce lasts until the „exit“ of the respective product from the market place.

Project vs. product manager
In case of a product development project, both the project and product manager need to work together.  Whereas the project manager is primarily responsible for the implementation of the product, the product manager is accountable and responsible for defining the product requirements, development, marketing and possibly sales and distribution of the product.  In this sense the product manager’s responsibilities go beyond those of the project manager.  After all, a product life cycle usually lasts longer than that of a project life cycle.
The question may arise to which extend a product manager needs to get involved in project manager.  It depends on the quality of project management.  At the end of the day it is the product manager who is accountable for the success of the product.  Hence, he/she must have more than a sincere interest that the project of the product development is running smoothly and delivers the desired results.  This implies that a good product manager should at least be knowledgeable of basic project management principles.  Ideally, a product manager has a solid project management understanding.  There may be cases where he/she has to make decisions escalated to him/her.  In this case, it is important to be able to read the complete project environment to come to a just conclusion.  In other cases, the product manager may be asked to coach or monitor the project manager.  In any case, it pays off for the product manager to know as much as possible about project manager based on own experience.
On the other hand, the project manager should have at least a basic understanding of the needs, expectations and processes of product management.  Often product management is the client of project management and its team.  Consequently, the project manager should treat product management as its client.

Buttom line, both the project and product manager need to work together in a team for the time of the project.  Roles and resonsibilities need to be clearly defined.  They must not interfere into each other’s realm of influence.  Instead, they should both strive for synergy effects and win-win outcomes.

On this token, please have a look at our white paper on requirements which can be downloaded from our website.