Zanetti graduated from the United States Military Academy, at West Point, in 1980. Following his graduation he served six years in the United Stated Army, before he shifted to the United States Army Reserves.
He was promoted to Brigadier General in 2005.
During his service at Guantanamo there was a high-profile controversy around the conduct of Brigadier General Thomas W. Hartmann. Hartmann had been appointed the legal advisor to the Convening Officer for the Guantanamo Military Commissions. His position required him to be a fair and neutral supervisor of both the Defense team and the Prosecution team. Nevertheless, when Colonel Morris Davis, then the Chief Prosecutor, went on leave, Hartmann usurped his role, and ordered Prosecutors to prepare charges against additional suspects beyond those Davis had chosen. When Davis returned, and tried to restore order to the Prosecution team, chaos ensued.
On August 13, 2008, at a pre-trial hearing prior to Guantanamo captive Mohammed Jawad's Guantanamo military commission. Carol Rosenberg, writing in the Miami Herald, quoted Zanetti characterizing Brigadier General Thomas W. Hartmann's approach to charging Guantanamo captives as:
- "Spray and pray. Charge everybody. Let's go. Speed, speed, speed."
According to Rosenberg Zanetti described Hartmann's treatment of his subordinates as:
- "abusive, bullying and unprofessional . . . pretty much across the board."
During his first six years of active service Zanetti earned a Masters degree in Finance, from Boston University. When he shifted from the regular army to the reserves he established himself as a financial advisor. Zanetti eventually broadcast a radio show on financial planning.
Zanetti's wife, Teresa Zanetti, was a state legislator, in New Mexico. In 2009 Zanetti considered running for Governor of New Mexico, and he officially announced his candidacy on June 14, 2021. Zanetti was the third member of the Republican Party to put their name forward as a possible candidate to unseat the current Governor, Michelle Lujan Grisham, a member of the Democratic Party. The two other Republicans who put their names forward have been Jay Block and Karen Bedonie. Incumbent Governors are rarely unseated in New Mexico.
Zanetti criticized Grisham's implementation of countermeasures to the Covid 19 virus. He argued his decades of experience in financial planning had left him with a good understanding of New Mexico's economy.
- "Greg Zanetti: About". Greg Zanetti for Governor, 2022. June 2021. Archived from the original on 2021-07-01. https://web.archive.org/web/20210701024109/https://zanettiforgovernor.com/about/. Retrieved 2021-07-01. "After six years of active duty, Zanetti earned his master’s degree in business from Boston University, and returned home to New Mexico. He went to work as a financial advisor for E.F. Hutton. Simultaneously, he continued to serve his country and joined the New Mexico Army National Guard. Greg became an independent financial advisor in 1991."
- Carol Rosenberg (2008-08-13). "Guantanamo general calls 2nd general 'bullying'". Miami Herald. Archived from the original on 2008-08-15. https://web.archive.org/web/20080815141730/http://www.mcclatchydc.com/251/story/48053.html. Retrieved 2008-08-13.
- Cheryl Dilgard (2008-02-15). "Zanetti connects money management skills to JTF mission here". Joint Task Force Guantanamo. http://www.jtfgtmo.southcom.mil/storyarchive/2008/08febstories/0202208-BGZanetti.html. Retrieved 2008-08-13.
- "NM NATIONAL GUARD HOSTS SEND OFF CEREMONY FOR SOLDIERS AND AIRMEN HEADED TO GUANTANAMO, CUBA". New Mexico National Guard. https://www.nm.ngb.army.mil/pad/MM/MinutemanSpring08.pdf. Retrieved 2008-08-13.
- Emily J. Russell (2009-01-02). "Beyond the standard: Joint Task Force deputy commander thanks Troopers for a job well done". The Wire (JTF-GTMO). Archived from the original on 2011-07-22. https://web.archive.org/web/20110722214250/http://www.jtfgtmo.southcom.mil/wire/wire/WirePDF/v9/Issue45v9.pdf. Retrieved 2009-01-09.
- Carol Rosenberg (2008-09-20). "General stripped of legal authority at Gitmo". Seattle Times (Washington, DC). Archived from the original on 2021-06-16. https://web.archive.org/web/20210616192309/https://www.seattletimes.com/nation-world/general-stripped-of-legal-authority-at-gitmo/. Retrieved 2021-07-01. "In August, a deputy prison-camp commander, Army Brig. Gen. Gregory Zanetti, testified that Hartmann was “abusive, bullying and unprofessional” and employed a “spray-and-pray” strategy to stage the tribunals in a crude compound called Camp Justice."
- "Gitmo Detainee Says He Was Tortured". Courthouse News Service. 2009-04-24. Archived from the original on 2021-07-02. https://web.archive.org/web/20210702010604/https://www.courthousenews.com/gitmo-detainee-says-he-was-tortured/. Retrieved 2021-07-01. "Here are the defendants: Donald Rumsfeld, Air Force General Richard Myers, Army Major General Geoffrey Miller, Army General James Hill, Army Major General Michael Dunlavey, Army Brigadier General Jay Hood, Marine Brigadier General Michael Lehnert, Rear Admiral Harry Harris, Rear Admiral Mark Buzby, Rear Admiral David Thomas, Rear Admiral James Stavridis, Army Lieutenant General McNeill, Army General Tommy Franks, Army Brigadier General Gregory Zanetti, Army Colonel Nelson Cannon, Army Colonel Terry Carrico, Army Lieutenant Colonel William Cline, Army Lieutenant Colonel Diane Beaver, Captain Carolyn Wood, George Tenet, Robert Gates, The Department of Defense of the United States, and The United States of America."
- Greg Boyd (2021-06-14). [https://web.archive.org/web/20210615002006/https://www.abqjournal.com/2399958/gop-field-evolving-as-greg-zanetti-announces-gubernatorial-bid.html https://web.archive.org/web/20210625170512/https://www.abqjournal.com/news/state/211052225515newsstate02-21-09.htm "GOP field evolving as Greg Zanetti announces gubernatorial bid"]. Albuquerque Journal. Archived from the original on 2021-06-25. https://web.archive.org/web/20210615002006/https://www.abqjournal.com/2399958/gop-field-evolving-as-greg-zanetti-announces-gubernatorial-bid.html https://web.archive.org/web/20210625170512/https://www.abqjournal.com/news/state/211052225515newsstate02-21-09.htm. "While Zanetti has been active in county-level politics — including two stints as Bernalillo County GOP chairman — and worked with several conservative groups, his only previous run for elected office came in 1994 when he unsuccessfully sought the Republican nomination for lieutenant governor."
- Jeff Jones (2009-02-21). "ABQJOURNAL NEWS/STATE: Greg Zanetti May Run for Governor". Albuquerque Journal. Archived from the original on 2021-06-25. https://web.archive.org/web/20210625170512/https://www.abqjournal.com/news/state/211052225515newsstate02-21-09.htm. "Longtime Albuquerque financial adviser and New Mexico National Guard Brig. Gen. Greg Zanetti is eyeing a Republican run for governor — bringing the current number of prospective or confirmed Republican and Democratic candidates for the 2010 race to four."
- "Military veteran runs for New Mexico governor as Republican" (in en-US). KRQE News 13 Albuquerque - Santa Fe (Santa Fe, New Mexico). 2021-06-14. Archived from the original on 2021-06-18. https://web.archive.org/web/20210618112230/https://www.krqe.com/news/politics-government/elections/military-veteran-runs-for-new-mexico-governor-as-republican/. "Zanetti has nurtured a public following on local radio with regular appearances to provide financial advice."