The Welwyn-based company will maintain more than 100 parks and open spaces and 42 play areas as the council's preferred bidder over Connaught Environmental, Wyevale Grounds Maintenance and the council's current grounds maintenance contractor Sodexho (Land Technology).
John O'Connor Grounds Maintenance managing director Matthew O'Conner said: "We will work hard to ensure we meet the trust the council has placed in us."
East Hertfordshire executive member for the environment and conservation Terence Milner said: "It was vital that we got the decision right, balancing the quality of work with offering the best possible value for money for our taxpayers. Our parks and open spaces are an important asset for residents, businesses and visitors alike, and this decision means they're in safe hands for the future."
The relationship could span two decades as the agreement is for an initial period of six years and nine months with an option to extend for a further seven years.