After returning to Bulawayo in 1947, he became a trade unionist for black railway workers and rose to the leadership of the Railway Workers Union and then to leadership of the African National Congress in 1952. In 1960 he became president of the National Democratic Party which was later banned by the Rhodesian government. He also became one of Rhodesia's wealthiest self-made entrepreneurs.
Joshua Nkomo was the target of two attempted assassinations. The first one, in Zambia, by the Selous Scouts, a pseudo-team. But the mission was finally aborted, and attempted again, unsuccessfully, by the Rhodesian Special Air Service (SAS).
ZAPU forces committed many acts of violence during their war to overthrow the Rhodesian government. The most widely reported and possibly the most notorious were when his troops shot down two Air Rhodesia Vickers Viscount civilian passenger planes with surface-to-air missiles. The first, on September 3, 1978, killed 38 out of 56 in the crash, with a further ten survivors (including children) shot by ZIPRA ground troops dispatched to inspect the burned-out wreckage. The eight remaining survivors managed to elude the guerrillas and walked 20km into Kariba from where the flight had taken off (it was headed for Salisbury, Rhodesia's capital, now renamed Harare). Some of the passengers had serious injuries, and were picked up by local police and debriefed by the Rhodesian army. The second shootdown, on February 12, 1979, killed all 59 on board. The real target of the second shootdown was General Peter Walls, head of the COMOPS (Commander, Combined Operations), in charge of the Special Forces, including the SAS and the Selous Scouts. Due to the large number of tourists returning to Salisbury a second flight had been dispatched. General Walls received a boarding card for the second flight which departed Kariba 15 minutes after the doomed aircraft. No-one has been brought to trial or charged with shooting down the aircraft due to amnesty laws passed by both Smith and Mugabe. In a televised interview not long after the first shootdown, Nkomo laughed and joked about the incident while admitting ZAPU had indeed been responsible for the attack on the civilian aircraft. In his memoirs, Story of My Life, published in 1985, Nkomo expressed regret for the shooting down of both planes.
Nkomo founded the National Democratic Party (NDP), and in 1960, the year British prime minister Harold Macmillan spoke of the "wind of change" blowing through Africa, Robert Mugabe joined him. The NDP was banned by Smith's white minority government, and it was subsequently replaced by the Zimbabwe African Peoples Union (ZAPU), also founded by Nkomo and Mugabe, in 1962, itself immediately banned. ZAPU split in 1963 and while some have claimed this split was due to ethnic tensions, more accurately the split was motivated by the failure of Sithole, Mugabe, Takawira and Malianga to wrest control of ZAPU from Nkomo. ZAPU would remain a multi-ethnic party right up until independence.
An unpopular government called Zimbabwe-Rhodesia, led by Abel Muzorewa, was formed in 1979 between Ian Smith and Ndabaningi Sithole's ZANU, which by now had also split from Mugabe's more militant ZANU faction. However, the civil war waged by Nkomo and Mugabe continued unabated, and Britain and the USA did not lift sanctions on the country. Britain persuaded all parties to come to Lancaster House in September 1979 to work out a constitution and the basis for fresh elections. Mugabe and Nkomo shared a delegation, called the Patriotic Front (PF), at the negotiations chaired by Lord Carrington. Elections were held in 1980, and to most observers' surprise Nkomo's ZAPU lost in a landslide to Mugabe's ZANU. The effects of this election would make both ZAPU and ZANU into tribally-based parties, ZANU with backing from the Shona majority, and ZAPU the Ndebele minority. Nkomo was offered the ceremonial post of President, but declined.
Finally after much debate and refusals, Nkomo was appointed to the cabinet, but in 1982 was accused of plotting a coup d'état after South African double agents in Zimbabwe's Central Intelligence Organization, attempting to cause distrust between ZAPU and ZANU, planted arms on ZAPU owned farms, and then tipped Mugabe off to their existence.
In a public statement Mugabe said, "ZAPU and its leader, Dr. Joshua Nkomo, are like a cobra in a house. The only way to deal effectively with a snake is to strike and destroy its head."
NKOMO FLEES: ZAPU leader, Joshua Nkomo, fled in self-imposed exile to London after illegally crossing the Botswana frontier disguised as a woman on March 7th. 1983, claiming that his life was in danger, and that he was going to look for “solutions” to Zimbabwean problems abroad.” (Government Printer, Harare 1984). "...nothing in my life had prepared me for persecution at the hands of a government led by black Africans." (Nkomo - My Life, p.1)In the aforementioned book, 'The Story of My Life', Nkomo ridicules the suggestion (page 4) that he escaped dressed as a woman. "I expected they would invent stupid stories about my flight..... People will believe anything if they believe that". After the Gukurahundi massacres, in 1987 Nkomo consented to the absorption of ZAPU into ZANU, resulting in a unified party called ZANU-PF, leaving Zimbabwe as effectively a one-party state, and leading some Ndebeles to accuse Nkomo of selling out. These Ndebele individuals were, however, in such a minority that they did not constitute a meaningful power base within the cross-section of ZAPU. In a powerless post, and with his health failing, his influence declined.
When asked late in his life why he allowed this to happen, he told historian Eliakim Sibanda that he did it to stop the murder of the Ndebele (who supported his party) and of the ZAPU politicians and organizers who had been targeted by Zimbabwe's security forces since 1982.
Nkomo had been an inactive member of the Missionary Church for most of his life. He converted to Roman Catholicism in 1999, shortly before he died of prostate cancer on July 1 at the age of 82 in Parirenyatwa Hospital in Harare.
On 27 June, 2000, a set of four postage stamps were released by the Post and Telecommunications Corporation of Zimbabwe featuring Joshua Nkomo. They had denominations of ZW$2.00, $9.10, $12.00 and $16.00 and were designed by Cedric D. Herbert.