1. a person or thing that is certain to succeed
a shoo-in for promotion/winning/victory
Someone who is 'a shoo-in' for something is certain to succeed or be a winner in a contest. You could be 'a shoo-in' for a particular role you are applying for, for example. This is a popular phrase used in business and social contexts, though it is slightly informal. Similar phrases include 'a sure thing' or 'a cinch'.