He said "profit" and "market share" were not dirty words but stressed that the Government would not compromise its values by allowing weapons to be sold to repressive regimes.
Dr Fox spoke to the Defence and Security Equipment International exhibition at the Excel Centre in east London as protesters staged demonstrations against British arms manufacturers.
The Defence Secretary said: "The United Kingdom's export licensing regime is amongst the most rigorous in the world.
"Respect for human rights and fundamental freedoms are mandatory considerations for all export licence applications, which we consider on a case-by-case basis.
"When conditions change we act swiftly to revoke licences that do not meet our strict criteria - just as we did earlier this year as the events in the Middle East and North Africa unfolded."
He added: "We will not compromise our values. But let me be equally clear, we will continue to support our allies and partners, we will help with their security needs, and we will support businesses seeking to do that."
In April MPs accused ministers of misjudging the risk that British arms exports to countries such as Libya and Bahrain would be used to repress their own people.
The Commons Committees on Arms Export Controls disclosed that as recently as last year, UK firms were given licences to sell equipment ranging from small arms and tear gas canisters to armoured personnel carriers to countries in the region.
Dr Fox noted that British defence companies support 300,000 jobs across the country, but said the best way to sustain the industry in the long-term was by boosting sales abroad.
"For too long export potential has been ignored when initiating projects for the UK's own use. That needs to change," he said.
"Exportability needs to become ingrained in the requirement setting, commissioning and production processes - because only through exportability can risks and costs be shared in a viable way."
Dr Fox also warned that budget cuts meant the Government would be a "tougher, more intelligent customer" of defence firms in the future.
He said: "The pressure on the public purse means that now more than ever, value for money for the taxpayer must be demonstrable.
"Value for money is not about compromising your defence aim or compromising business viability - it is about realising those aims in a way that is sustainable for both customer and supplier. That balance has not always existed in the past."
Meanwhile, campaigners have won the right to protest against the Defence and Security Equipment International exhibition - one of the world's biggest arms fairs - after a blanket ban on marches in the area was lifted.
The prohibition came into force on September 2 as a response to concerns about a demonstration planned by far-right group the English Defence League (EDL) in the east London borough of Tower Hamlets.
But the Metropolitan Police applied for permission to vary the ban to allow an anti-arms trade march from Westminster to the Excel Centre to take place tomorrow after a threat of legal action from campaigners, according to solicitors Christian Khan.
Protesters say at least 14 delegations to the arms fair have come from countries defined as "authoritarian regimes" by human rights groups.
They have expressed dismay that those invited include officials from Bahrain, which has killed scores of citizens since protests broke out in February.
Matthew Knowles, spokesman for ADS, the UK's aerospace, defence and security organisation, said: "The defence industry directly employs over 110,000 people across the whole country and supports over 300,000 jobs in total, generating more than £22 billion for the UK economy in 2010.
"With tough, effective and industry-supported Government export controls in place, it is clear that defence is delivering for the UK economically while meeting the concerns of society."
