Which two signers of the Declaration of Independence later became US presidents? The two Declaration signers who became President were John Adams (2nd US President) and Thomas Jefferson (3rd US President).(The Benjamin Harrison (V) who signed the Declar … ation was the father of 9th President William Henry Harrison and the great-grandfather of 23rd President Benjamin Harrison.).n Founding Fathers. The two Declaration signers who became President were John Adams (2nd US President) and Thomas Jefferson (3rd US President).