Despite his tenure at Citigroup, Wall Street is suspicious of Lew's lack of "significant experience in financial regulatory matters and the financial markets," said Washington analyst Brian Gardner with Keefe, Bruyette & Woods.
"While he can undoubtedly learn the material on the job, we question whether he has sufficient relationships with the banking industry in the U.S. and abroad, which can be critical during a financial crisis," Gardner said in research note.
Lew also worked as a financial administrator at New York University from 2001 to 2006.
Lew received an undergraduate degree at Harvard University and a law degree from Georgetown University.
Lew has developed a reputation as a details guy, who regularly logs in 16 hour days at the White House. He observes the Jewish Sabbath of leaving work before sundown on Friday and abstaining from work on Saturdays. However, he is known to have worked Saturdays in urgent situations.
The White House didn't respond to requests for comment.