LAS VEGAS—Oil billionaire T. Boone Pickens, who on Wednesday endorsed presumptive GOP nominee Donald Trump, is planning to host a fundraising event for the pro-Trump super PAC next month, the first major effort by the super PAC to raise money.

Mr. Pickens, chairman of the hedge fund BP Capital, has invited Ed Rollins, the co-chairman of the super PAC, to visit his Texas ranch in mid-June, along with a few other fundraising officials from the group. The goal is both to raise money for the super PAC and to bolster party unity,...