The Low-Key British Newshound Taking Charge of The Washington Post

In the swashbuckling world of British newspapers, the editor Robert Winnett stands out for his lack of flash. Taciturn and low key, more likely to be buried in documents at his desk than hobnobbing at a Mayfair club, Mr. Winnett, the deputy editor of The Daily Telegraph, is known for his focus on breaking news, once earning the nickname “Rat Boy” for his relentless drive for scoops.

Now Mr. Winnett is stepping into a spotlight that will be hard to avoid: This fall, he will become the editor of The Washington Post, taking over one of the most powerful and scrutinized jobs in American journalism at a pivotal time in the news industry.

His ascent is due to his longstanding ties to Will Lewis, the chief executive of The Post. Mr. Lewis, a Fleet Street star, mentored Mr. Winnett at The Sunday Times of London and later at The Telegraph, where Mr. Winnett spearheaded a groundbreaking investigation into fraudulent expenses that led to the resignations of scores of British politicians.

But Mr. Winnett remains an unknown quantity, both in elite American media circles and within the newsroom he will soon lead. He will arrive at The Post after 17 years at The Telegraph, a center-right paper associated with Britain’s Conservative Party. Some of his past practices, including the payment of a six-figure sum to obtain the documents crucial to the expenses investigation, run counter to the more stringent reporting ethics followed by American news organizations.

Representatives of The Post declined to make Mr. Winnett available for an interview.

But interviews on Monday with former colleagues and Fleet Street veterans presented a portrait of a scoop-obsessed journalist with a distaste for dinner parties and a passion for the Chelsea soccer