Japan’s SoftBank Group Corp. is poised to launch the world’s biggest technology fund as early as Saturday, capping months of arduous negotiations in which the tech giant haggled with the fund’s main Saudi investor over control of the money, investment strategy and questions about its commitment.

The birth of the Vision Fund, which is expected to start with just under $100 billion in investments and a 12-year term, ushers a huge, new force into a tech-investment world long dominated by Western bankers and Silicon Valley financiers....