A spokeswoman for Adler's law firm confirmed his death on Monday.
Adler had been at the University of Pennsylvania hospital since last month, when he underwent emergency surgery for an infection in the tissue around his heart.
Adler, a Democrat, served one term in Congress before being defeated in November by former Philadelphia Eagles lineman Jon Runyan.
Congressman Runyan released this statement: "May those he left behind be comforted in the knowledge that his lifetime of public service to our community has left a lasting legacy for which they can be most proud."
Adler was the first Democrat to represent his traditionally Republican 3rd Congressional District in more than a century.
Before being elected to Congress, he was a state senator and Cherry Hill councilman.
Republicans and fellow Democrats mourned his passing Monday, with GOP Gov. Gov. Chris Christie describing Adler as "a fine public servant and a good person."
Assembly Speaker Sheila Y. Oliver said "Congressman Adler was a true example of what it means to serve the people."
Senator Diane Allen said "His intellect and energy was a benefit to his constituents and all who had the honor of serving with him."
Adler leaves behind a wife, Shelly, and four children.
The Associated Press contributed to this report.
