Serco Group said chief operator officer Ed Casey will leave the group at the end of the year.
Casey wishes to return to the US and has accepted a role with another company, which is not a competitor, Secro said.
He will stand down on 31 December 2017.
"Whilst we are very sad that Ed is leaving, we completely understand that after four years of weekly commuting across the Atlantic, he would like to have a job closer to home," Serco chief executive Rupert Soames said.
At 8:01am: (LON:SRP) Serco Group PLC share price was +0.75p at 117.75p