He was a former Pinkerton's detective and a former cop hired by Cal's father to take care of him.
Lovejoy was also the only one that suspected that Jack had not savedRose DeWitt Bukater from falling upon Lovejoy and Dawson's first meeting, noting that he already had untied his shoes and removed his coat .
He is seen later running after Jack and Rose as they ran at the engine room. While descending with the elevator, Rose gave him "the finger". Possibly becuse it was the moment where he started hating them.
Lovejoy asked the Titanic's Man-at-arms to take Jack into custody in E Deck. There, knowing that the ship was sinking, and seeing that the E Deck had been evacuated, he left Jack tied there, although later Rose saved him.
For the most part Lovejoy is seen looking for Jack and Rose, especially after Cal put his coat (with the Heart of the Ocean in its pocket) on Rose. Cal took Lovejoy's gun and started shooting at them, until his bullets were wasted. Cal gave it back to Lovejoy saying that the diamond would be his. Lovejoy then loads the gun and goes hunting for them in the dining room. He was looking for them in the dining room but Jack caught him off guard and crushed a glass window with his head and punched him as they ran away.
He is last seen at the point where the Titanic is breaking in half, with a large gash on his forehead from his battle with Jack. It is unknown what happens to him after that but it is likely that he fell between the ships crack.
He is not seen at the end, among the people seen by Rose among the Titanic victims. This is likely because he was one of the two major villains, as Cal was not there either.
In the theatrical version, the scene where Lovejoy is looking for Jack and Rose in the first-class dining room was cut from the film as it was considered too long. His last appearance with a bleeding head seems unexplained in the cut version.