For most people, yes, you will need a fishing license. The most important thing to remember is that each US state has control of licensing in their freshwater and nearshore saltwater fishing. So the rules around fishing licenses vary by each state.
There are some general trends, however:
When fishing offshore outside of state control, the federally required National Saltwater Angler Registry still applies. For most people, this will be included with their state issued fishing license. If you are an edge case that's not automatically covered, you will need to register with NOAA.
To find out the license requirements for the state you want to fish in, you can check out the controlling state agency's website. The names vary by state (Fish & Game, Department of Natural Resources, etc). You can also check out Take Me Fishing which is a non-profit that has licensing overview for each state.
Fishing Fundamentals