Shields, 49, of Captain Cook is a minister in the Religion of Jesus Church, founded in 1969 by James Kimmel.
In 1994, Shields aided police when they raided his house, voluntarily showing them 7.9 ounces of marijuana and admitting it was his.
But he said he had a right to marijuana because it is a sacrament in his church, and he is guaranteed its use by the U.S. Religious Freedom Restoration Act of 1993.
The law has several hurdles a believer must clear before he or she is protected. Shields was apparently tripped by the requirement that his religion must mandate the use of marijuana.
Shields and others testified that the use of marijuana is important in their religion, but not required.
Circuit Judge Ronald Ibarra sentenced Shields to a 90-day suspended jail term and a year's probation.
Shields could have received a year in jail and a $2,000 fine.
Shields said he will appeal. He will also meet with church elders, including Kimmel, and determine whether to make marijuana mandatory for members.
He said he didn't like the idea philosophically.
"We practice freedom of choice as part of our belief system," he said.
But as a practical matter, a marijuana mandate may be necessary to protect believers, he said.
Deputy Prosecutor Melvin Fujino had formally agreed with Shields and his attorney Jack Schweigert that Shield's belief is sincere.
Shields testified he grew up in the First Christian Church but later became an agnostic or atheist. While smoking marijuana at Kaena Point on Oahu in 1972, "I discovered God personally," he said.
Prosecution witnesses testified marijuana is harmful and addictive, giving government a "compelling" reason to ban it.
Defense witness Blaise Harris, a psychiatrist, quoted the Merck Manual, which Schweigert described as a medical "bible," which said marijuana is not addictive.
Toxicologist William Albrecht testified that a recent University of California at Los Angeles study shows smoking marijuana does not lower lung functions as tobacco does.
Tobacco smokers who also smoke marijuana also avoid the loss of lung function, he said.