The gift of the gab
Definition 1 of 1
Pro Tip 1/3Persuasive Skill
It refers to the talent for convincing others through fluent and appealing speech. 
Jason used the gift of the gab to sway the audience.
Pro Tip 2/3Not Always Honest
Sometimes implies using words to deceive or manipulate, rather than being truthful. 
Be careful; the con artist's gift of the gab can seem credible.
Pro Tip 3/3Informal
This idiom is casual and might not be suitable for formal situations or written documents. 
At the informal meeting, her gift of the gab was quite effective.