Councillor Ged Hall, who represents the Burn Valley ward, left Labour in 2016 after a series of run-ins with the party and stood as an independent.
Now, Councillor Hall, who has represented Burn Valley for 18 years, has decided to rejoin the party.
Councillor Hall said: “It is clear that both nationally and locally the Labour Party has changed.
"Here in Hartlepool we have talented new councillors from all walks of life who are absolutely committed to improving our town.
“The leadership team of Brenda Harrison and Jonathan Brash have brought decency and integrity back to the Labour Party in Hartlepool and I am proud to join this wonderful team who are offering new ideas and a new vision for our town.”
The Labour Group has welcomed Councillor Hall, who met with his new colleagues for the first time this week.
The leader of the Labour Group, Councillor Brenda Harrison, said: “We are delighted that Ged has chosen to join the Labour Party and will now be a member of the Labour Group of councillors.
“His many years of service to Hartlepool are testament to his character and commitment to our town and I am really looking forward to working with him.”
Councillor Harrison has also suggested the door is open for other independent councillors who may want to cross the floor.
She added: “We know that there are a lot Independent councillors who are very upset with the way the Conservatives are running Hartlepool and we are always open to a conversation with those councillors who share our values.”