Finding qualities in project managers which may make them good leaders isn't terribly difficult. After all, any project manager worth their pudding is already planning ahead, understands their teams, and is willing to go the distance when it comes to project success. But great leaders also need to be able to “strategise, negotiate, network, calculate risk, and collaborate to get the job done,” as explained in this article by Dan Matthews.
The key, according to the article, is finding the right people who both understand the root of project management and are also able to quickly communicate to the people working with them in order to complete projects. It's easy to confuse what a leader is compared to a manager in terms of definition, but not nearly so much when it comes to results: a manager is able to keep the ship floating, while a leader is able to guide the ship through rough seas and uncharted oceans.