Angus grew up in Britain, Ceylon and Kenya. After serving the Royal Marines, he settled in Australia and had a number of jobs. During middle age, he suffered from financial hardship and fell victim to a number of confidence tricks for which he took the blame. He was known for his friendly and outgoing personality, and his few speeches in the House of Lords were viewed positively.
Angus was born on 9 October 1938 as the son of Alexander Montagu, 10th Duke of Manchester, and Nell Vere Stead, and was the younger brother of Sidney Montagu, 11th Duke of Manchester. He was born in the family seat of Kimbolton Castle near Bedford but moved frequently during childhood, including spending time in Singapore and Ceylon including a period in a convent in the latter. He did not enjoy his time there, later saying the nuns "weren't very pleasant people".
In 1950, he joined his father in Kenya for a short period after Kimbolton was sold. He had a good relationship with his mother, who enjoyed looking after young children, and was spoiled as a result. After trying the local school in Keyna, but was bullied and stopped going, and consequently had no regular formal education until he was eleven. He was subsequently educated at Trearddur House, Trearddur Bay, Anglesey, a Welsh prep school and Gordonstoun School, Moray, Scotland, returning each summer to Kenya to spend time with his family. He left school in 1956 without any qualifications and began service in the Royal Marines, boarding HMS Loch Fyne in January 1957. He was the only public-school educated man on the ship and did not get on well with his fellow recruits.
Upon discharge, he had jobs in the oil industry and in tourist-related activities across the United States. He moved to Australia in 1959 and was variously employed as a clothes salesman, a barman, and a crocodile wrestler. He later spent time in Canada and by 1968 had moved into a bedsit in Bedford, England, near Kimbolton.
As a hereditary peer, the Duke was able to take a seat in the House of Lords and made his maiden speech there on 25 November 1991, in a debate on the European Union. Though the speech was only three minutes long, it was praised for its brevity and succinctness by other peers, including Viscount Tonypandy. He also raised questions about redundancies in the Armed Forces with the Leader of the House of Lords, Viscount Cranborne.
The Duke was good friends with celebrity photographer Allan Warren. Together, they established the Duke's Trust, a charity for children in need. Towards the end of his life, the Duke set up the company Unique Tours, to show American tourists places such as Stratford Upon Avon. He found that customers liked meeting a genuine English peer.
The 10th Duke's business venture in Kenya failed, reducing the family estate from millions to £70,000. By time of his father's death, the new duke had little money, and his warm and outgoing personality made him vulnerable to fraudsters and confidence tricksters.
In 1985, Angus was arrested for conspiracy to commit fraud against the National Westminster Bank for £38,000. He inherited the title of Duke of Manchester while awaiting trial following the death of his brother. He was acquitted after he was ruled to be insufficiently competent and intelligent enough to conduct and organise the raid, and had been set up to take the blame. The trial judge said of him "on a business scale of one to 10, the Duke is one or less, and even that flatters him".
In 1991, the Duke became honorary chairman of the Tampa Bay Lightning ice-hockey team, pledging to raise $25 million. He was also chairman of a holding company based in Dublin, Link International, which was responsible for raising the money. The company failed, unable to pay significant debts, and in 1996 the Duke was convicted of fraud. At the trial, his defence lawyer argued that he was the victim of a confidence trick by a business partner. He was jailed for 33 months and served 28, following which he was deported back to Britain.
On 22 November 1961 at Geelong, Australia, Angus married Mary Eveleen McClure, daughter of Walter Gillespie McClure of Geelong, who had been a director of General Motors Holden. There were three children of the marriage: Alexander Charles David Drogo Montagu (born 1962), Lord Kimble William Drogo Montagu (born October 1964) and Lady Emma Montagu (September 1965 – 29 April 2014). They were separated in 1965 and divorced in 1970; she continued to style herself Duchess of Manchester.
Angus walked out on Mary days after the latter birth, and did not have a proper relationship with Emma until 20 years later, when he regained contact with her and Kimble. He remained distant from Alexander, and attempted to bar him from inheriting the title of Duke of Manchester. Emma briefly lived with Angus in his Bedford flat in the early 1990s.
On 5 March 1971, Angus married Diane Pauline Plimsaul of Wimborne, Dorset, daughter of Arthur Plimsaul of Corfe Mullen. They were divorced in 1985, after Montagu had inherited the dukedom, and his second wife is now Diane, Duchess of Manchester. On 27 January 1989, Manchester married Anne-Louise Taylor (known as Louise), formerly Mrs Bird, daughter of Dr. Alfred Butler Taylor of Cawthorne, Yorkshire. They were divorced in 1998, following his incarceration. She is now Anne-Louise, Duchess of Manchester. At the time of the Duke's death, he was attempting to reconcile with Louise.
On 22 April 2000, at the Swedish Church, Mayfair, in London, the Duke of Manchester married the former fashion model Biba Hiller (born Jennians on 3 February 1942), but they were divorced the following year. Biba, Duchess of Manchester, died of cancer aged 61 on 11 October 2003.
Angus had been a close friend with Jane Probyn (now Jane Bishop) and they were briefly informally engaged around 1960. They remained friends for the rest of his life. He was friends with Keith and Kerry Cheeseman from the early 1970s until his death.
In later life, Angus had a fraught relationship with his elder brother Kim, the 11th Duke. Upon the death of Andrea, Kim's second wife, in 1996, Angus discovered she had changed the will so that the entire estate would go to her eldest child (the 11th Duke's stepson) and the 12th Duke would receive nothing.
The Duke died of a heart attack at home on 25 July 2002, aged 63. At the time of his death, his estate had a net deficiency, and he weighed over 22 stone (140 kg). His funeral took place at Bedford Crematorium on 5 August, with his children Kimble and Emma, and ex-wives Diane and Louise in attendance.
The House of Lords Act 1999 largely abolished the rights of hereditary peers to sit in the House of Lords with some limited exceptions; the Duke of Manchester was not among them. He was succeeded by his eldest son, Alexander.1938–1985: Lord Angus Montagu
1985–2002: His Grace The Duke of Manchester
The Duke was also 15th Earl of Manchester, 15th Viscount Mandeville and 15th Baron Montagu of Kimbolton.