The Pew Charitable Trust started in 1948 as the Pew Memorial Fund. This fund started when the four children of Joseph N. Pew, the founder of Sun Oil, decided to take their seven individual charitable funds and merge them into one much larger trust fund.

The Pew Memorial Fund was established to honor Joseph N. Pew and his wife Mary Anderson Pew, it was set up by their two sons, J. Howard Pew and J.N. Pew Jr.; as well as their two daughters Mary Ethel Pew and Mabel Pew Myrin.

There are two sources of income for the fund, the first being the fact that the trust is the sole beneficiary of the seven funds that the Pew children founded. The second is the fact that upon founding, the trust was given a share of Sun Oil Company stock.

The Pew Memorial Fund started handing out grants anonymously, and between 1948 and 1956 they made 181 grants grossing over $12.5 million. In spite of the desired anonymity, requests for grants and funding increased tremendously. It soon became clear that a full time staff of people equipped to handle the paperwork involved, as well as to handle the assets, would be necessary. In response to this need, the Glenmede Trust Company was created in 1956. The new trust was formed to allow the Pews to create individual and specific funds that fit their philanthropic interests while still allowing other people to control the everyday aspects of controlling a fund.

The Sixties brought prosperity to the Pew Charitable Trusts, it marked a time of wide growth. Their yearly grant average was $5 million, an increase of four times the amount that was giving before then. Despite the economic and political instability, the Pew Trusts gained during the '60's.

The growth trend continued into the Seventies, and in spite of the change of leadership that took place by the end of the decade they were still able to give 3,500 grants that totaled over $296 million. This amount is five times the amount that was given just ten years before. The Seventies also brought a change in focus, as the fund grew the area of philanthropy grew as well. Philadelphia based organizations were still important, but they were no longer the prime focus as the trust looked outward, this also notes their move from anonymous giving.

The Eighties brought even more change, as for the first time ever the Trust published an annual report. In addition they began to issue guidelines to prospectives seeking grants; they began to define activities that they would consider for grants. Instead of giving grants to organizations that met specific needs in an area, the Trust started a more proactive role of developing their own programs to meet those needs. Over a progression of years, Trust-initiated programs began to take over issue areas, and became highly focused means for addressing problems. In addition to transition, the trust also grew, going from $296 million in grants to $1.13 billion divided among 5,000 grants. Between 1990 and 1999 the Trusts gave out the same amount of grants (5,000), but increased the funding to $1.83 billion.

The latest change took place January 1, 2004. The Trusts underwent a legal change in structure that formed them into an official independent public charity. This change should allow improvements in operation and effectiveness.