37-year-old Glenn Goodman was shot while on duty on 7 June 1992 when he made a routine stop of a vehicle on the A64 near Tadcaster.
He died later that day. Paul Magee, a member of the IRA, was jailed for life for his murder but later released under the Good Friday agreement.
The officer, who was married and had a young son, had only been with North Yorkshire Police for eight months at the time of the shooting.
His patrol partner, Pc Sandy Kelly, was also shot and injured but recovered.
The private gathering in Tadcaster today was attended by serving police officers and former colleagues.
North Yorkshire Chief Constable Dave Jones said: “Glenn’s death was a dark and tragic moment in the history of North Yorkshire Police and he will never be forgotten.
“Glenn was volunteering to help protect his local community when he - and his family - paid the ultimate price.
“Today there are thousands of others on duty across the UK, facing similar dangers every day who all deserve our support and respect.
“Poignantly, the anniversary of Glenn’s death falls within National Volunteers’ Week, when we pay homage to volunteers across the country who, to use Glenn’s own words, do it ‘to make a difference’.
“My thanks goes to each one of these remarkable people, while the thoughts of everyone at North Yorkshire Police remain with Glenn’s family and friends.”
After the shooting on June 7, 1992, Pc Kelly – a policeman for 11 years and married with two children – radioed for help in spite of his injuries.
Just 15 minutes after the shooting a second police patrol car was riddled with bullets as it pursued the gunmen’s car near Burton Salmon, just off the A162.
Four days after Glenn Goodman was killed, Magee and his colleague Michael O’Brien were arrested in Pontefract as they broke cover and tried to evade the police dragnet.
On March 30, 1993, Magee was jailed for life at the Old Bailey. The judge, Mr Justice Laws, recommended that Magee should serve a minimum of 30 years. O’Brien was jailed for 18 years.