Caseby, who has served five secretaries of state at the department during his tenure, has been headhunted to be a partner in a management consultancy specialising in the Gulf region.
He declined to name the company but revealed that the work could involve some comms and strategy work.
Towards the end of his tenure, Caseby said he had been working on assignments in the Middle East, setting up comms teams in countries where the UK has strategic partnerships, such as Jordan.
While in Jordan he led a project for the country’s prime minister, co-ordinating comms across all ministries and developing strategy.
He also advised Oman’s Council of Ministers on creating the country’s first comms team, which launched in October.
During his tenure at DWP, Caseby trained and mobilised a team of 150 job centre managers to speak to regional media every month about employment levels and changes to the welfare system, which generated sustained coverage in print, broadcast and online.
He also set up a digital team from scratch that now produces in-house video, design, graphics and gifs for all social media channels and that has increased DWP’s Twitter following tenfold, to 280,000.
Caseby said that a recent Cabinet Office review of DWP comms had revealed it to be one of the highest performing teams in Whitehall, adding that it showed "evidence of best practice in all functions".
Commenting on the colleagues he worked with for four years, Caseby said: "I'm really proud of the DWP team – they're young, talented and driven."
DWP’s work has been controversial and the introduction of Universal Credit, the increased use of benefit sanctions and links made between sanctions and the use of food banks have attracted negative media coverage.
But Caseby, a former managing editor of The Sunday Times and The Sun, became known as a tough defender of the Government’s welfare reforms and was nicknamed Iain Duncan Smith’s "pitbull" by The Guardian for his efforts.
He was unapologetic about the efficacy of the reforms, telling PRWeek: "I’m returning to the private sector at a time when Universal Credit is on track after a positive Budget. The changes were absolutely necessary to ease people's transition into the new benefit. I joined as a believer, and I leave as one."
Caseby’s last day at DWP is Friday and he will be replaced by interim director of comms John Stevenson, who has been seconded from his role as head of media at the Department for International Trade to take up the job until a permanent director of comms is appointed in the coming months.