Uber hasn't disclosed exactly how much SoftBank will invest, but Reuters reports that Uber will receive $1 billion (£765 million) in funding and SoftBank will purchase $9 billion (£6.8 billion) of existing shares.
But the Japanese firm voiced caution, saying: "While the SoftBank Group side is considering an investment in Uber, there is no final agreement at this stage".
In a separate statement, Uber said if conditions on share price and minimum shares are not "satisfactory" for the SoftBank group, "there is a possibility" that it may not make an investment.
Currently Uber's largest shareholder is USA venture capital firm Benchmark with a 13 percent stake and founder Travis Kalanick who has a 10 percent stake.
Uber has struck a multi-billion dollar deal led by investment companies Softbank and Dragoneer. "We believe this agreement is a strong vote of confidence in Uber's long-term potential".
Uber's chief of policy for India and South Asia has quit, two sources familiar with the matter said on Monday, in the latest high-level departure at the online taxi company.
Uber argued that once in the bag, the investment would help fuel its development in the tech sector and its continued expansion at home and overseas, "while strengthening our corporate governance".
The Japanese group, founded by billionaire Masayoshi Son, expressed an interest several months ago in investing around $1 billion in Uber for a stake of at least 14 percent.
A deal would be positive for Uber, which is looking ahead to the future in the wake of recent repeated scandals, among them workplace sexual harassment allegations. The investment deal with SoftBank will likely cause Benchmark to drop its suit, Reuters reported.
SoftBank is sending tremors through the tech world with its massive new Vision Fund, a venture capital fund intended for startups and expected to dominate the industry before long.