free agent
n. A person who works for him- or herself and is not a permanent employee of a corporation.
Are you self-employed? Your retirement options aren't limited to individual retirement accounts, Keoghs, or similar defined-contribution plans. Entrepreneurs, consultants, and other free agents are establishing traditional defined-benefit pension plans — the sorts that large corporations provide their employees.
—Susan Garland, “Now the Self-Employed Can Sock Away More,” Business Week, July 30, 2001
Daniel H. Pink is young, fresh and evangelistic. His book, "Free Agent Nation" (Warner Business Books, New York, 2001, $24.95), is an irrepressibly enthusiastic view of what he embraces as the most profound change in work life since Americans fled the farm for jobs in industry. Mr. Pink is pleased to declare that the job as we know it — 9-to-5, with indefinite tenure — is drying up, a relic of the industrial age.

The new system is people working for themselves — "the growing ranks of people who work but don't hold a job." By a conservative count, 33 million Americans now make their living as "free agents." They work on their own, or as temporary hires, or as employees of tiny enterprises of only three or four people. (There are 13 million microbusinesses today, most of them based at home.) By Mr. Pink's definition, one American worker in four is already a free agent.
—Fred Andrews, “Not Holding a Job Is New Work System,” The New York Times, May 27, 2001
1993 (earliest)
With the building blocks of the economy literally at their fingertips, increasing numbers of Americans are escaping the bureaucracies of the industrial economy. No longer cogs in the wheel, they are becoming free agents.
—Cheryl Russell, “The Master Trend: How the Baby Boom Generation Is Remaking America,” Plenum Publishing, September 01, 1993
Another high-stress category is the younger, "free agent" manager, or, as Atlanta psychologist Bob Bleke calls it, the "corporate vagabond." Well trained and upwardly mobile, the free agents go from firm to firm, seeking the biggest challenges and the highest salaries.
—Annetta Miller, “Stress on the Job,” Newsweek, April 25, 1988