A former top civil servant at the Home Office has settled his employment tribunal claim against the government.
Announcing his departure, Sir Philip accused the home secretary of a “vicious and orchestrated briefing campaign” against him.
Ms Patel has rejected all claims of bullying that have been made against her.
It is understood that the government agreed a “substantial” payout with Sir Philip, reportedly a six-figure sum.
Sir Philip, who was claiming “constructive dismissal”, said in a statement released through the FDA union: “I am pleased to say that the government has today settled the claims that I brought against them and which were due to be heard in an employment tribunal in September.”
He added: “This settlement resolves my own case. The FDA is continuing to pursue in separate proceedings the wider issues that have been raised.
“I now look forward to the next stages of my career.”
The government said it “regrets the circumstances surrounding Sir Philip’s resignation”.
“The government and Sir Philip are now pleased that a settlement has been reached to these proceedings,” it said in a statement.
A Home Office spokesperson said: “The government and Sir Philip’s representatives have jointly concluded that it is in both parties’ best interests to reach a settlement at this stage rather than continuing to prepare for an Employment Tribunal.
“The government does not accept liability in this matter and it was right that the government defended the case.”
A 10-day tribunal had been scheduled to begin in September.
Referencing reports that Sir Philip had agreed a six-figure settlement with the government, Labour’s shadow home secretary Nick Thomas-Symonds said: “Taxpayers will be appalled at having to pick up the bill for the home secretary’s unacceptable behaviour.
“The home secretary still has very serious questions to answer about her conduct and the FDA union’s legal case continues.
“The prime minister has shown terrible judgement. It can’t be right that his adviser on ministerial standards resigned when he found that the home secretary bullied colleagues, while the home secretary herself remained in post.”
Sir Philip said he had received allegations against the home secretary that included her “shouting and swearing, belittling people, making unreasonable and repeated demands – behaviour that created fear and that needed some bravery to call out”.
He said he was not interviewed as part of an inquiry which found that Ms Patel had bullied staff.
Boris Johnson overruled the conclusion of Sir Alex Allan, his adviser on ministerial standards, that the home secretary had breached the ministerial code.
Sir Alex resigned from his role in the aftermath of the prime minister’s move.
The FDA, which represents senior civil servants, has launched a judicial review to try and overturn the PM’s decision to stand by Ms Patel and disregard the findings from Sir Alex.