Mariner scored 139 goals in 339 games for Ipswich in a golden era in which they won the FA Cup in 1978 and UEFA Cup in 1981.
His other clubs included Plymouth, Arsenal and Portsmouth while he also earned 35 England caps and scored 13 times for his country.
Mariner had been battling brain cancer.
A statement from his family read: "We regretfully inform you that Paul passed away peacefully on July 9 surrounded by his family, after a brief battle with brain cancer.
"We would like to thank all the people who came to see him through his illness for their support and for the messages that were sent to him, they meant a great deal to him and us.
"A special thank you must go to the NHS and the unbelievable care he received when he most needed it and for that we, as a family, will forever be in your debt.
"Paul lived a full life and was fortunate enough to represent a group of fantastic football clubs as well as his country, all of which meant the world to him.
"Anyone who knew Paul will attest to his fantastic sense of humour, his passion for life and for his work.
"He will be sorely missed by everyone who was ever around him and by those most close to him."
Mariner also had playing and coaching spells in the United States and he managed Plymouth during the 2009-10 season.
A tweet from Ipswich read: "We are devastated to hear the news of the passing of Town legend Paul Mariner at the age of 68.
"The thoughts of everyone at #itfc are with Paul's family and friends at this sad time."
A tweet from the England team’s account read: "We're sad to have learned that Paul Mariner, who made 35 appearances for the #ThreeLions , has passed away at the age of 68.
"Mariner represented England between 1977 and 1985, scoring 13 goals.
"Our thoughts and sympathies are with his family, friends and former clubs."
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