His decision was taken "after many weeks" of what he describes as "wrestling" with himself.
As a "dyed-in-the-wool Eurosceptic", he concedes the decision may surprise some people.
He has consistently opposed European political integration, in particular EU "meddling" in defence, and taken a tough stance on immigration.
On Thursday, the MEP, a retired British army official, also admitted that he has spent "many years" in Brussels opposing "so much" of EU policy.
But he insisted he was not an automatic 'outist', adding, "I have found the black or white decision on Remain or Leave especially difficult. Like most of the British people, I have no affection for the EU. But I am recommending that we Remain."
He added, "In my view, Britain has now carved out a special position in the EU while retaining our seat at the top table. The importance of our economic links and the fragility of the international economic system demand stability and confidence, not unnecessary risk.
"The answers to many of our problems rest with the British government, not Brussels. The Prime Minister is committed to enhancing Britain's role in the world beyond the EU. I have taken account of each of these factors in coming to my decision."
He went on, "The immigration issue is becoming the most contentious issue. As I have tried to explain for many years - most immigrants to Britain do not come from the EU countries. We are not bound by EU asylum and immigration rules. Control of non-EU immigration is entirely the responsibility of British government."
The veteran deputy said that in the period 1998-2015, non-British net immigration to the UK was a "massive" 4,887,000.
Of these 1,333,000 (27 per cent) were from the EU and 3,553,000 (73 per cent) from the rest of the world.
"The discussion of this issue has been distorted. I have long called for a rigorous Royal Commission on Immigration to look at all aspects of the problem.
"Under the arrangements that have now been negotiated, we would be outside many of the parts of the EU that we find objectionable, while able to take advantage of those parts which benefit us.
"Staying in avoids an economic shock and enables us to build on clear areas of British exceptionalism.
"It is up to the British government, not the EU, to stimulate more business activity outside Europe, to tackle the problems of migration from Africa, the Middle East and Asia, to reform our human rights obligations, to invest more in technological research, to continue to enhance our military and diplomatic capabilities, and to keep our economy successfully on track.
The 71-year-old said, "After 23 June, we can forestall any moves by the EU to take further powers; we can rigorously exploit the exceptional terms that we have marked out; and we can continue the push for reform; let us remain and have the best of both worlds."
Van Orden, first elected an MEP in 1999, still wants a cut in Britain's massive financial contribution to the EU (second only to Germany), and proper control over borders.
Some members of Van Orden's ECR group have openly defied David Cameron and announced their intentions to campaign for Brexit.
They include Amjad Bashir, who nevertheless insisted that; "This is not a vote against Europe or its people; it is a vote borne out of deep frustration with the EU's chronic inability to achieve the reforms it critically needs, not just to prosper, but to survive as a political entity."
Bashir's colleague Emma McClarkin, who serves as the ECR group's shadow rapporteur on TTIP, also supports of Brexit.
However, most Conservative MEPs are expected to vote in favour of remaining a member of the EU.
Vicky Ford, Chair of Parliament's internal market and consumer protection committee, highlighted that, "the single market helps the UK trade across Europe's 500 million consumers."