Downing Street described the former ambassador to Moscow, who will now play a key role in the UK's Brexit talks, as a "seasoned and tough negotiator," the BBC wrote.
Sir Ivan's exit, which came earlier than planned, sparked a row with his resignation note criticizing "muddled thinking" from ministers.
Read alsoBBC: Some MPs "ready to vote against triggering Brexit"Some MPs had accused him of being "half-hearted" towards Brexit.
Critics of the outgoing ambassador were accused of trying to "politicize" the civil service, with a trade union saying there was a "deafening silence" from ministers in defending officials' independence.
Sir Tim was the UK's ambassador to Moscow from 2011 to 2015. He has also advised a succession of foreign secretaries as well as holding other roles in the UK's EU mission.
