Be in the driving seat
Definition 1 of 1
Pro Tip 1/3Authority Symbol
The phrase often symbolizes having authority or influence in a situation. 
She was in the driving seat of the negotiation, leading the discussion.
Pro Tip 2/3Positive Connotation
Using this phrase suggests a favorable view of the person in control. 
Ever since Helen took the driving seat, the project has been a success.
Pro Tip 3/3Leadership Context
It's commonly used when someone takes a leadership role, especially in business or team scenarios. 
Mark is in the driving seat now, so all decisions go through him.