Heaton, 21, started his career at Preston North End, but was released by the SkyBet Championship side in the summer of 2016.
In his ten years at Preston, he also had loan spells at Tamworth and Colne.
He then joined Droylsden and Stalybridge Celtic before switching to Bamber Bridge last summer.
He played for the Quakers in pre-season, but a proposed move then broke down because of injury.
In October this year, he moved on to Ramsbottom, making three appearances for them.
Darlington manager Tommy Wright told the club`s Ray Simpson: “I feel that we need a bigger presence in the centre of our defence. I tried to get Josh when he was at Preston, but he was tracked by several other clubs as well, and I missed out. He was also watched by several bigger clubs in his Preston career as well. He has got experience of this league from his days at Tamworth and Stalybridge.”
Heaton goes straight into the squad for the away game at Kidderminster Harriers tomorrow.