Karen Ward will join the Treasury to serve as Hammond's special economic adviser.
Prior to joining the government, Ward had been at HSBC for more than a decade, and her appointment comes as Hammond prepares for his first fiscal event as chancellor - the Autumn Statement on 23 November.
Previous people to hold similar roles include Ed Balls, who advised former prime minister Gordon Brown when he was chancellor, and went on to serve as a cabinet minister.
In June Ward was the lead author of an HSBC report which said Britain's vote to leave the EU would act as a "major drag" on eurozone demand, as Britain was the destination for 13% of eurozone exports.
"Potential disruption to supply chains and a general cloud of uncertainty may also weigh on growth in trade, and in turn business investment," the report said.
Separately, Brexit secretary David Davis has also added to his team with the appointment of a prominent think-tank expert.
Open Europe's Raoul Ruparel will join Davis' team imminently having contributed to the economically liberal policy experts' work since 2008.
The think tank maintained a neutral stance in the run up to the referendum, although it has previously advocated a slimmed-down European Union.