Priti Patel, who has for decades fought for British departure from the EU, has returned to the Cabinet and become the fourth woman to head the Ministry of Interior.
Mr Johnson's office confirmed in a tweet late on Wednesday evening that Ms Patel had been appointed Home Secretary.
A diehard Thatcherite and a key supporter of Mr Johnson, the pro-Israel MP has been give the post despite her chequered background.
Ms Patel voted to leave the EU in 2016, has called Brussels undemocratic and supports a no-deal Brexit.
Theresa May made Ms Patel the International Development Secretary when she became prime minister in July 2016.
In November 2017 Ms Patel was forced to leave the role after it emerged she had held secret talks with Israeli officials that year.
The MP, who has long had a close relationship with Israel, met Yair Lapid, leader of the Yesh Atid party, while on holiday.
Ms Patel was accompanied by Lord Polak, honorary president of the lobby group Conservative Friends of Israel.
She was accused of failing to tell the Foreign Office she discussed official business on what was declared a private holiday, and for conducting “freelance” diplomacy.
When the news broke of her secret meetings Ms Patel was ordered back to London by Mrs May for a confrontation, with about 22,000 people tracking her return online.
She initially hit back and said she had done nothing wrong, but eventually, accepted that the political fallout was too great and resigned.
“I accept that in meeting with the organisation and politicians during a private holiday in Israel that my actions fell below the high standards that are expected of a Secretary of State,” she wrote in her letter to Mrs May.
“While my actions were meant with the best of intentions, my actions also fell below the standards of transparency and openness that I have promoted and advocated.”
Despite this, she will return to the front bench as Mr Johnson tries to modernise and diversify the image of the Conservative Party.
Ms Patel’s parents were from Gujarat, India, and moved to Uganda. They left in the 1960s, not long before President Idi Amin threw out Asian minorities.
She has been among Mr Johnson's biggest cheerleaders and has being doing the media rounds for the new prime minister.
“Boris spoke very clearly during the leadership contest of having a modern Conservative Party, with all the talents that represent all aspects of the Conservative Party,” she told ITV on Wednesday morning.
“I’ve no doubt that’s exactly what he’ll do in government , to deliver Brexit but actually take us beyond Brexit and to all the domestic issues your viewers are so focused on – education funding, more police officers on the streets.”
