From Longman Dictionary of Contemporary Englishfree agentˌfree ˈagent noun [countable] someone who is not responsible to anyone else and can do what they want
Examples from the Corpus
free agent• Dexter signed with the San Diego Chargers as a free agent in 1986.• He got that when George signed as a free agent in February.• You can be a free agent, trading or stealing, building or fighting.• In that case X is not a free agent, but it is not yet clear whether Y is one.• Charnley is now a free agent.From Longman Business Dictionaryfree agentfree ˈagent a person or organization that is free to do what they want, without legal or other restrictionsAfter the contract expires, they will be free agents, producing movies at various studios. → agent 