The Brighton-born 28-year-old, who had been interesting Barnsley, will stay at the Amex Stadium until the end of the 2014/15 season, which will see him complete 10 years with the club.
"I'm absolutely delighted to have signed the new deal," he told the club's official website.
"I love playing for the club and I can't wait for the season to start now.
"I've been keeping myself fit in the gym and although it's not the same as doing pre-season, I feel really good and I'll definitely be fit for the start of the season.
"The last 10 years have been amazing and I feel really honoured to have been granted a testimonial year by the club."
El-Abd has made over 250 appearances for Brighton since he made his first-team debut in 2003.