Matthew Hanley, 23, was jailed at the Old Bailey for 12 months for his part in the 2015 crime.
His associate, Connor Allsopp, 21, was sentenced to eight months in jail for his lesser role in the hack.
In court, Judge Anuja Dhir QC said it was a tragedy to find “two individuals of such extraordinary talent” in the dock.
She told the pair: “You were both involved in a significant, sophisticated systematic hack attack in a computer system used by TalkTalk.
“The prosecution accept that neither of you exposed the vulnerability in their systems, others started it, but you at different times joined in.”
The court had heard that the 2015 hack had cost the company £77m, although this figure was reached by the company’s chief financial officer and not an independent body.
TalkTalk was fined a record £400,000 for its shoddy security practices over the incident.
At the time, an investigation by the Information Commissioner’s Office (ICO) declared that insufficient security at the company allowed customer data to be accessed “with ease”.
The ICO found that TalkTalk could have prevented the data breach in October 2015 if the firm had taken basic steps to protect customers’ information.
“For no good reason, TalkTalk appears to have overlooked the need to ensure it had robust measures in place despite having the financial and staffing resources available,” the ICO report concluded.
The hack saw the personal details of 156,959 customers accessed, including their names, addresses, dates of birth, phone numbers and email addresses.
The company was again fined £100,000 last year when another ICO investigation found customer data was being used by scammers at a call centre in India.