Though initially an Order of poor monks, the official papal sanction made the Knights Templar a charity across Europe. Further resources came in when members joined the Order, as they had to take oaths of poverty, and therefore often donated large amounts of their original cash or property to the Order. Additional revenue came from business dealings. Since the monks themselves were sworn to poverty, but had the strength of a large and trusted international infrastructure behind them, nobles would occasionally use them as a kind of bank or power of attorney. If a noble wished to join the Crusades, this might entail an absence of years from their home. So some nobles would place all of their wealth and businesses under the control of Templars, to safeguard it for them until their return. The Order's financial power became substantial, and the majority of the Order's infrastructure was devoted not to combat, but to economic pursuits.

By 1150, the Order's original mission of guarding pilgrims had changed into a mission of guarding their valuables through an innovative way of issuing letters of credit, an early precursor of modern banking. Pilgrims would visit a Templar house in their home country, depositing their deeds and valuables. The Templars would then give them a letter which would describe their holdings. Modern scholars have stated that the letters were encrypted with a cipher alphabet based on a Maltese Cross; however there is some disagreement on this, and it is possible that the code system was introduced later, and not something used by the medieval Templars themselves. While traveling, the pilgrims could present the letter to other Templars along the way, to "withdraw" funds from their accounts. This kept the pilgrims safe since they were not carrying valuables, and further increased the power of the Templars.

The Knights' involvement in banking grew over time into a new basis for money, as Templars became increasingly involved in banking activities. One indication of their powerful political connections is that the Templars' involvement in usury did not lead to more controversy within the Order and the church at large. Officially the idea of lending money in return for interest was forbidden by the church, but the Order sidestepped this with clever loopholes, such as a stipulation that the Templars retained the rights to the production of mortgaged property. Or as one Templar researcher put it, "Since they weren't allowed to charge interest, they charged rent instead."

Based on this mix of donations and business dealing, the Templars established financial networks across the whole of Christendom. They acquired large tracts of land, both in Europe and the Middle East; they bought and managed farms and vineyards; they built massive stone cathedrals and castles; they were involved in manufacturing, import and export; they had their own fleet of ships; and at one point they even owned the entire island of Cyprus.