Mr. McMillen received his Bachelor of Science degree in Government from Florida State University in 1976, and his Doctor of Law degree from Emory University in 1979. He is a member of The Florida Bar (since 1980) and the State Bar of Georgia (since 1979).

He is rated "AV" by the widely referred to Martindale-Hubbell Law Directory. The "A" represents "legal ability", and is the highest score given, defined by Martindale as "very high to preeminent". The "V" score represents "adherence to professional standards of conduct and ethics, reliability, diligence and other criteria relevant to the discharge of professional responsibilities." It is also the highest score given.  He is also a member of the Million Dollar Advocates Forum, and has been featured in Leading American Attorneys in the field of medical malpractice.

Mr. McMillen is involved in numerous bar association activities including: The Orange County Bar Association (President 1999-2000; Executive Council 1993-96,  Medical-Legal Committee Chairman 1991, 1993);The Legal Aid Society (President 1996-97, Board of Trustees, 1993-96).  He has served as a member and Chairman of the Judicial Nominating Commission for Florida's Fifth District Court of Appeals.  In 2006 he was the President of the Central Florida Trial Lawyers Association.  He is a member of The American Bar Association (Fellow of the American Bar Association Foundation); The Florida Bar (Board of Governors 2008-2009,Technology Task Force 2002, Attorney Grievance Panel 1994-1996 - Chair 1996,Trial Lawyers Section, Health Law Section); Florida Justice Association a/k/a Academy of Florida Trial Lawyers (Medical Malpractice Task Force, Committee Chairman, 1997-98); the American Association for Justice a/k/a Association of Trial Lawyers of America (Birth Trauma Litigation Group, HMO Litigation Group, and Laparoscopic Surgery Litigation Group).  

Mr. McMillen is a frequent lecturer to other lawyers and to the medical profession about medical malpractice issues. He currently serves as the author of the monthly medical malpractice law column in the Journal of the Florida Justice Association (Academy of Florida Trial Lawyers).  Other important publications include   "The Overlooked Emergency Room Cause of Action" Vol. LXXI, No. 10 The Florida Bar Journal (Nov. 1997), and "Medical Malpractice Statute of Limitations" Vol. LXX, No. 2 The Florida Bar Journal (Feb. 1996).