More than 1,280 executives, including directors from 51 FTSE 100 companies, have signed a letter backing the UK's membership of the EU.
The Remain camp said the letter to the Times showed "unprecedented" support from across business and finance.
Many signatories have already expressed support, but Remain said new names include Sir John Parker from Anglo American, and Barclays' John McFarlane.
Companies on the list employ 1.75 million people, Remain said.
Wednesday is the last official day of campaigning ahead of the UK's in/out referendum on its membership of the European Union, with voters going to the polls on Thursday.
In the joint letter, the bosses say: "We know our firms are stronger in Europe. Our reasons are straightforward: businesses and their employees benefit massively from being able to trade inside the world's largest single market without barriers.
"We know that Britain leaving the EU would mean having to re-establish terms of trade from scratch with our home market of 500 million consumers. That wouldn't just hurt exporters but the hundreds of thousands of small and medium firms who do business with them.
"Even those that want Britain to leave say that, in the short-term, Brexit would lead to economic uncertainty and would put jobs at risk. Smaller businesses and the people they employ are particularly vulnerable to any economic shock which could follow a vote to leave the EU.
"Britain leaving the EU would mean uncertainty for our firms, less trade with Europe and fewer jobs.
"Britain remaining in the EU would mean the opposite - more certainty, more trade and more jobs. EU membership is good for business and good for British jobs. That's why, on 23 June, we back Britain remaining in the EU."
Polls suggest that while big business is broadly in favour of staying in the EU, small firms are evenly split.
But Remain said its list included some 900 small businesses, ranging from a salt maker in Anglesey, dairy farmers in Devon, printers in Antrim and whisky distilleries in the Scottish Highlands.
Other high profile executives to come out in support of staying in, include Tony Pidgley from Berkeley Group, Standard Life's Sir Gerry Grimstone, and Bruce Hemphill, at Old Mutual.
The group said that such an overwhelming show of support from UK businesses puts to bed the claim of Leave campaigners that "business is split" on the Europe issue.