(Adds deal details in paragraphs 2, 4, 5 & 6; CEO comment in paragraph 3, ESI background in paragraph 7)

June 28 (Reuters) - Electronic equipment maker Keysight Technologies said on Wednesday it would acquire a controlling stake in French software firm ESI Group in a 913 million euros ($995.81 million) deal.

California-based Keysight will pay 155 euros per ESI share in cash, a 72% premium to its closing price on May 17, when ESI disclosed preliminary discussions with some third parties on a possible acquisition of the firm.

"Keysight's acquisition of ESI Group accelerates our strategy of providing software-centric solutions with virtual prototyping and advanced simulation capabilities," Keysight CEO Satish Dhanasekaran said in a statement.

Keysight has entered exclusive negotiations with some shareholders of ESI Group, representing an aggregate of 50.6% of ESI's share capital and 55.8% of the theoretical voting rights.

Once the deal is completed, Keysight will launch a mandatory tender offer for the remaining outstanding shares of ESI Group, it said.

Th deal will increase Keysight's software revenue and annual recurring revenue, or ARR, Keysight said in a statement.

ESI Group provides services in more than 15 countries and has about 1,000 employees.

($1 = 0.9168 euros) (Reporting by Lavanya Ahire in Bengaluru; Editing by Subhranshu Sahu and Rashmi Aich)