Born to an English father and Scottish mother, Crosby was raised in Newbury, Berkshire, studied at Leeds University and the University of Cardiff's School of Journalism.

After graduation Crosby joined the BBC becoming a producer on its rolling news channel, BBC News 24. Moving on from there, she worked for News Direct 97.3 and LBC before joining The Money Channel in 1999.

In 2001, she joined CNBC Europe and became a presenter on European Market Wrap. She also spent some time in the United States while with the network and reported for its early morning show Squawk Box, where her mentor was Maria Bartiromo. She joined Sky in 2003 presenting the early morning news programme, Sunrise, and in October 2007 became a London correspondent on the Fox Business Network.

At Sky News she regularly co-presented the channel's weekday Sky News Today, the Friday morning edition of Sunrise and some weekend broadcasts. She was also the channel's Business correspondent.

In January 2009 she moved to the ITV breakfast programme GMTV on a reported salary of £120,000, replacing long serving presenter Fiona Phillips, who quit after 16 years. On 1 August 2010 it was announced that Emma was leaving GMTV, with the impending launch of Daybreak which replaced GMTV.

In October 2010 in an interview with the Daily Record, Crosby confirmed that she will present on CNN, before returning to BBC News.