Aug 13 (Reuters) - Australian stock exchange operator ASX posted a more than 5% rise in annual underlying profit on Thursday as global market volatility lifted trading activity, sending its shares towards their biggest daily gain since 2020.

The stronger earnings come as ASX works to rebuild trust after months of intense regulatory scrutiny over a string of operational failures, and a downgrade by ratings agency S&P.

Regulators have questioned its management of critical market infrastructure, prompting increased investment in technology upgrades and system resilience.

The bourse operator said global market volatility bolstered trading activity and demand for post-trade services during the year ended June 30. That helped the markets division log an 18.6% rise in revenue, with futures and options volumes up 14.4%.

"The second half of FY26 saw exceptionally active and volatile markets, driven primarily by global events," ASX said in a statement.

"ASX recorded its highest month of futures trading volume ever and the second-largest equities trading day ever by number of executed trades."

Annual underlying net profit after tax rose to A$536.4 million from A$510 million a year earlier. The company declared a final dividend of 104.7 Australian cents per share.

Shares of ASX rose as much as 9.9% to A$61, posting their biggest intraday percentage gain since March 17, 2020 and hitting their highest level since May 7.

"At first take, we see this as a sound result driven by slightly better-than-expected top line revenue," Citi analysts said in a note.

ASX's total expenses rose 21.1% to A$557.4 million due to increased spending on technology modernisation, additional technology capabilities and costs associated with a corporate regulator inquiry.

The bourse operator spent heavily on its Clearing House Electronic Subregister System, or CHESS, clearing platform despite several outages and a scrapped overhaul.

Citi said they now await "firmer strategic directions from the new CEO who starts on September 1."

ASX has tapped Euronext's Anthony Attia as its next chief executive, opting for an international appointment over an internal candidate to repair its damaged reputation.

($1 = 1.4158 Australian dollars)

(Reporting by Rajasik Mukherjee; Editing by Subhranshu Sahu)