Governors in Nigeria introduced the criminal aspect of Islamic law as a political tool, according to the pressure group, Human Rights Watch.
Sharia was very popular in the north when introduced
Governors in the north of Nigeria are using Sharia, while at the same time condoning human rights abuses under the system, Human Rights Watch said.
Twelve northern Nigerian states have introduced Sharia since the year 2000.
The move initially heightened tensions between Muslims and Christians and led to clashes which left thousands dead.
The 111-page report documents the way in which human rights have been violated in the four years since the introduction of Sharia criminal law.
Ten people have been sentenced to death and dozens of others have been sentenced to amputation and flogging.
Many of these people, the report says, have been tried without adequate legal representation, convicted on confessions extracted under police torture and sentenced by judges who are improperly trained.
However, Human Rights Watch acknowledges that such abuses are at least as common in Nigeria's non-Sharia legal system.
A judicial official in Zamfara state - the first to introduce Sharia in 2000 - rejected the criticism.
"Sharia is our way of life, and no amount of criticism by people who hate it will make us change it," said Musa Bello.
Women face particular discrimination, the group says, pointing to cases such as that of Amina Lawal, the mother sentenced to death by stoning for adultery and only released after an international outcry.
For adultery, the standards of proof are different for men and women and judges have failed to investigate allegations of rape made by female defendants.
Sharia has also led to restrictions in women's social freedoms, Human Rights Watch says.
Many amputations sentences have not been carried out
"State governments and Sharia courts... have concentrated on the harsh aspects of Islamic law while ignoring its principles of generosity and compassion," said Peter Takirambudde, executive director of Human Rights Watch's Africa division.
Sharia criminal law was extremely popular in the north when it was first introduced, with many Muslims hoping it would deliver an improved justice system.
Instead, Human Rights Watch argues, it has been used by northern governors to gain political advantage.
The BBC's Anna Borzello in Nigeria says that popular support for the more extreme forms of Sharia punishment has now faded.
Human Rights Watch says that of the more than 60 amputations sentences carried - mostly for theft - it could only confirm that two had been carried out, both in Kano state.
However, for as long as these laws remain on the statute book, they can be revived and implemented at any time.