The 32-year-old formerly held the title world business editor and is the first woman to hold the City post since the Sunday broadsheet launched five years ago. She replaces Robert Bailhache, who has moved to Financial Dynamics.
Pfeifer's remit will have an international focus, according to the papers publisher Andrew Neil.
'It is not a traditional City editor in the style of the Sunday broadsheets or dailies,' he said.
'She is there to generate international business stories, on French or Spanish telecom firms as much as BT, for example. The joy is that London is a hub for everything that happens in investment banking, be it bond issues, equities or M&As. It is a good listening post.'
Explaining other changes of content at The Business, Neil said he harboured plans for beefing up the paper's New York operation, but would also look to cover more UK media stories, 'to get the major participants to notice us, to get us talked about'.
Neil admitted The Business wanted more contact from financial PROs: 'That is our fault rather than theirs. We still have to do more to get on everybody's radar. We're below the horizon for many people. We are working on it, developing a reputation as a reliable, authoritative international newspaper, but that takes time.'
The original idea behind Sunday Business, as it was before the 2002 relaunch, has been seen to fail, Neil said. 'Making Sunday Business into a bigger and better business section than the traditional market was not enough. You could still get pretty good coverage elsewhere.'
The Business has therefore recast itself as a rival to such publications as The Wall Street Journal, Financial Times and The Economist. Neil said: 'That is a pretty formidable peer group, but none of these comes out on Sunday.'
Pfeifer will report to executive editor Ian Watson. She joined at the paper's launch in 1998 as petrochemicals reporter from US trade title Chemical Week.