The 33-year-old has agreed a two-year deal at the Matchroom Stadium, and arrives following three years at Sky Bet League Two side Crawley Town.
A local boy to E10, Harrold was born in Leyton and started his career at Southend United where he signed his first professional contract in 2001.
Despite being handed the deal, the striker was unable to make the breakthrough at Roots Hall and enjoyed loan spells at Grays Athletic and Wingate & Finchley before signing for Harlow Town.
Following a year at Harlow, Harrold then joined Brentford and during his time with the Bees was loaned to Dagenham & Redbridge and Grimsby Town before joining Yeovil Town in 2005.
It was at Huish Park that the forward enjoyed his first taste of consistent first team football, making 48 appearances and scoring nine goals for the Glovers throughout the 2005-06 season before earning a deadline day move to Southend United on August 31, 2006 following a summer of interest.
Harrold’s return to Roots Hall saw him accumulate 38 appearances in his first season for the Shrimpers in the Championship, before adding another 21 the following season prior to joining Wycombe Wanderers on a free transfer in September 2008.
The striker went on to register 22 goals from 77 appearances during his two years with the Chairboys, earning a move to Shrewsbury Town ahead of the 2010-11 season.
During his year-long stay at New Meadow, the forward registered nine goals in 47 appearances before moving to Bristol Rovers.
Having notched 18 goals during his debut season for the Pirates, Harrold went on to make a total of 87 appearances during his three years at the Memorial Stadium, and in 2014 moved to Crawley Town.
The striker accumulated 80 appearances for the Red Devils, and even had a brief spell as caretaker manager at the Checkatrade Stadium at the end of last season.