The 22-year-old, who rose to national attention a year ago playing for England against the Barbarians, made a try scoring full debut for England last summer against Argentina and has subsequently appeared against South Africa and Wales this season.
Commenting on the signing, Leeds Director of Rugby Phil Davies said: "Phil is an extremely exciting young player and I am delighted that he has agreed to join us.
"His development in the last year with his performances for Bristol and England has shown that he has a big future in the game and hopefully he can continue that development with us over the coming years.
"Phil is capable of playing on the wing or at centre and he will be a key addition to our squad for next season."
Christophers was a near ever-present for the Shoguns during their doomed Premiership campaign, appearing in Bristol's starting line-up 20 times and scoring four tries.
A former Leicester Tigers Academy member, he spent a year playing in the French championship with Brive, a tough season which saw the famous club relegated, but one which matured the player, who was born and raised in the German city of Heidelberg.
He joins a Leeds side containing exciting England 'A' wing Dan Scarbrough, as well as Scotland fly-half Gordon Ross and England lock Tom Palmer, although the Tykes have lost star centre and goal-kicker Braam van Straaten to the Sharks recently.