Roche would pay $27 per share for Ignyta, representing a premium of about 74 percent to the stock's closing price on Thursday, they said.
Ignyta will continue its operations in San Diego and will be responsible for the ongoing pivotal study of entrectinib, its most advanced drug.
The U.S. company has a suite of drugs in early stage development that use gene therapy to kill off the underlying diseases that drive cancer tumor growth.
Reuters reported on Thursday Ignyta was in advanced talks to sell itself, just three years after the company went public with focus on precision drugs and diagnostics.
The deal is expected to close in the first half of 2018, the companies said. Citi advised Roche on the deal, while BofA Merrill Lynch and J.P. Morgan Securities LLC advised Ignyta.
Sidley Austin LLP and Latham & Watkins LLP were legal counsel to Roche and Ignyta, respectively.