Her Majesty's Penitentiary (HMP), located in St. John's, Newfoundland and Labrador, Canada is the primary facility for housing medium and maximum security male prisoners in Newfoundland and Labrador.

According to media reports, the name of the prison remains "Her Majesty's Penitentiary" as of September 2023, notwithstanding the death of Queen Elizabeth II and accession of King Charles III the previous year.

The Victorian-era structure is among the oldest operating prisons in Canada and has been criticized for its conditions including rat infestation and mould. Construction of a new facility to replace it was announced in 2019 but the commencement of construction has been continually delayed. Most recently, construction was to begin in the spring of 2023 and was to be completed within three years.

HMP St. John's is the largest prison in the province of Newfoundland and Labrador, by size and inmate population. Originally constructed in 1859, it houses primarily male offenders and has a capacity of 175 inmates. It is believed to be the oldest prison currently operating in Canada since the closure of Ontario's Kingston Penitentiary, in September 2013. Located in the Eastern district of St. John's, it is commonly referred to by locals as, Her Majesty's Hotel, or The Inn by the Lake, due to its proximity to Quidi Vidi Lake, which hosts North America's oldest annual sporting event, the Royal St. John's Regatta.

Despite its age, HMP St. John's, has undergone extensive renovations and additions, that provide inmates with modern cells, common areas and amenities. The province is responsible for the operation and administration of Newfoundland and Labrador's correctional service under the Department of Justice and Public Safety.

Notable escapes On December 12, 1964, four inmates escaped from HMP St. John's, by scaling a wall. The four prisoners stole a car and made their way to Whitbourne, Newfoundland and Labrador, where they encountered RCMP Constable Robert Westen Amey. The 24 year-old mountie, attempted to arrest one of the four escapees, Melvin Young, who shot and killed Amey. Cst. Amey, was the second RCMP officer to be killed in the line of duty in the province. On August 3, 2000, Richard Ryan became the subject of a Canada wide man-hunt after escaping from a Newfoundland and Labrador correctional officer, who was escorting Ryan to visit his sick mother. Described by police as a sexual sadist, Ryan eluded capture for 25 days, before being located in a makeshift camp in a wooded area near Long Harbour, Newfoundland and Labrador.

Notable inmates Father James Hickey, a former Roman Catholic priest, who was convicted of multiple sex crimes against children in Newfoundland and Labrador. Hickey was the first of numerous Roman Catholic priests and brothers, who were convicted of sex crimes in relation to a sex abuse scandal that rocked the province, and gained international infamy. While briefly held in HMP, Hickey would go on to serve the remainder of his sentence in Dorchester Penitentiary, New Brunswick, where he died in 1992. Michael Harris, a well-known journalist and former editor of Newfoundland and Labrador's now defunct Sunday Express, which was largely credited for breaking the scandal, would go on the publish a best selling book regarding the Mount Cashel sex abuse scandal. Paul Watson is an internationally known conservationist and founder of the Sea Shephard Conservation Society. In 1980, Watson was sentenced to ten days in prison for assaulting a fisheries officer, while attempting to disrupt the Newfoundland and Labrador seal hunt. Watson served his sentence at HMP St. John's. Vito Rizzuto, also known as Teflon Don, was a Mafia boss, and head of the notorious Rizzuto crime family, based in Montreal, Quebec. In 1987, Rizzuto was arrested following a drug bust in Trinity Bay, in an abandoned community called Ireland's Eye, where 225 million dollars of hashish was seized by RCMP. Rizzuto was remanded into HMP St. John's, before being released after a supreme court judge ruled that the RCMP had overstepped its surveillance efforts by wiretapping a meeting between Rizzuto and his attorney. Brian O'Dea is a former international drug smuggler who gained notoriety when he placed an advertisement in Canada's National Post seeking a job. The advertisement was titled "Former Marijuana Smuggler" and read: "Having successfully completed a 10-year sentence, incident free, for importing seventy-five tons of marijuana into the United States, I am now seeking a legal and legitimate means to support myself and my family. Business experience: Owned and operated a successful fishing business -- multi-vessel, one airplane, one island and processing facility. Simultaneously owned and operated a fleet of tractor-trailer trucks conducting business in the western United States. ... I also participated in the executive level management of 120 people worldwide in a successful pot-smuggling venture with revenues in excess of $100-million US annually." O'Dea, served prison time in California, Springhill Institution, NS, and HMP St. John's. Leo Puddester, was a former correctional officer and union leader when he was sentenced to four months in prison for defying a court order in relation to a wildcat strike he led in 1999. Puddister served his sentence at HMP St. John's, under the guard of the correctional officers he represented in labor relations with the Newfoundland and Labrador government. Puddester would go on to lead the province's largest public sector union, the Newfoundland and Labrador Association of Public and Private Employees (NAPE). In 2004, Puddester led the province's then twenty-thousand public sector workers on strike, leading to several public feuds with Newfoundland and Labrador's then premier, Danny Williams. Shirley Turner, a former medical doctor who was accused of killing her former boyfriend Andrew Bagby, in Keystone State Park, Pennsylvania, US. After Bagby's body was discovered, Turner fled to her home province of Newfoundland and Labrador, initiating a prolonged extradition process by US authorities. Turner, who was pregnant with Bagby's child, later gave birth to Zachary Bagby, which initiated a child custody battle between Turner and Andrew Bagby's parents, David and Kathleen Bagby. Released from prison on appeal of her extradition hearing, Turner murdered Zachary and then took her own life. David and Kathleen Bagby, along with their supporters were highly critical of the court process that lead to Turner being released from prison, and her ability to maintain custody of Zachary. Their activism and fight for justice led to the passage of Bill C-464, also known as Zachary's Bill, strengthening the conditions for bail in Canadian courts in cases involving the well-being of children. In 2008, Kurt Kuenne, a documentary filmmaker, and childhood friend of the Bagby family produced an award-winning film based on the murders of Andrew and Zachary, called Dear Zachary: A Letter to a Son About His Father. David Bagby would go on to author a book detailing the events, and his family's struggles with the Newfoundland and Labrador justice system. Leo Crockwell, was a 55-year-old Newfoundland and Labrador man when charged with five counts of attempted murder by the RCMP, after holding RCMP at bay for more than a week in a well-publicized police stand-off at a Bay Bulls home in 2010. Crockwell was able to escape the home, undetected, despite heavily armed mounties covering the perimeter of the house. Crockwell was arrested by the Royal Newfoundland Constabulary after hitching a ride to St. John's, where he told the driver of the vehicle he was travelling in, who he was. The incident was highly publicized and was a major embarrassment for the national police force. The Crockwell stand-off cost the RCMP just under half a million dollars, and its failure was the subject of an internal RCMP investigation, a book that outlined the events and the event itself remains public fodder in local lore. Crockwell was ultimately sentenced to four years in prison, which was served at HMP St. John's. Nelson Hart, was charged with two counts of first degree murder in June 2005, for the drowning deaths of his twin daughters in 2004, and was convicted in March 2007. In September 2014, an appeal court granted Hart a new trial. In July of that same year, the Supreme Court of Canada ruled that evidence obtained against Hart in a RCMP led "Mr. Big", operation was inadmissible. After the ruling, prosecutors declined to seek a retrial, and Hart was released from prison after serving nine years. The Supreme Court ruling led to stricter and more defined rules in the use of Mr. Big sting operations. Hart served his sentence partly in Newfoundland and Labrador's prison system. In 2015, journalist Colleen Lewis published a book in relation to the ordeal. Sean Buckingham, was a medical doctor with a well-established practice in downtown St. John's. In May 2005, Buckingham was arrested for a variety of criminal offences, in relation to providing prescription drugs, primarily Oxycontin, to drug addicted patients in exchange for services such as sex. In 2008, Buckingham was sentenced to seven years in prison, serving his sentence at HMP. Ed Byrne is a former politician and member of the House of Assembly for Newfoundland and Labrador. Byrne, who once led the provincial Progressive Conservative Party of Newfoundland and Labrador, was sentenced to a two-year prison sentence for fraud related crimes in connection with a constituency spending scandal. Byrne served his prison sentence in Newfoundland and Labrador's prison system. Wally Andersen is a former politician and member of the House of Assembly. A member of the Liberal Party of Newfoundland and Labrador, Anderson was sentenced to 15 months in prison for forgery and breach of trust, in relation to the constituency spending scandal. Anderson served his sentence in Newfoundland and Labrador's prison system, and later returned to politics, winning the mayor's seat of Happy Valley-Goose Bay, in 2018. Randy Collins is a former politician and member of the House of Assembly. Collins, who was a member of the Newfoundland and Labrador New Democratic Party, was sentenced to 21 months in prison for fraud related charges in relation to the constituency spending scandal. Collins served his prison sentence in Newfoundland and Labrador's prison system. Jim Walsh is a former politician and member of the Newfoundland and Labrador House of Assembly. Walsh, who was a member of the Newfoundland and Labrador Liberal Party was sentenced to 22 months in prison for fraud and breach of trust, in relation to the constituency spending scandal. Walsh served his sentence in Newfoundland and Labrador's prison system.