The chancellor is being urged to make "transition, trade and talent" a central commitment to the government's Brexit strategy as part of the City's Budget wishlist.
The wishlist, from the City of London Corporation, also calls on Philip Hammond to set parameters for future tax changes, lower the tax rate for corporate treasury centres and pledge to a host of measures to boost London's competitivity.
In an open letter to the chancellor, policy chairman Catherine McGuinness said "competitiveness, certainty and connectivity" were the three priorities.
"The next few years will be historically defining for the City, for London as our capital and for the country at large," she said. "This period will be crucial for the financial and professional services industry in the UK too, for the role they play both domestically and of course internationally.
"On the renewed world stage, where new markets present opportunities, and where the Corporation and firms are already innovating in areas such as fintech and green finance, financial services have a huge amount to contribute to the future economic growth and success of the UK."
McGuinness' letter was published as TheCityUK chief executive Miles Celic told the House of Lords the Prime Minister must agree a transitional deal ahead of a final trade agreement.
"From our point of view, it’s not much use getting to the end of the process and then being told there's a terrific transitional agreement here because any company... will have made their [contingency] decisions by that point."