Ben Lyon of 20th Century-Fox saw the pictures and signed Norma Jeane to a one year contract in 1946. He asked her to change her name. She considered reversing her names and adding an 'N' to her first name i.e. Jean Norman, (she loved the name Jean, it was also the name of her idol Jean Harlow) and for a while Carol Lind seemed the name that she would take. Eventually (after her own suggestion of Jean Monroe had been turned down) Marilyn Monroe was agreed upon. She later said:
'I often wish I had held out for 'Jean Monroe', I've never liked the name Marilyn...' She only two small film roles before she was dropped by the studio. Marilyn had a bit-part in 'The Shocking Miss Pilgrim' in 1947 but she was uncredited, most of her work ended up on the cutting room floor and Scudda Hoo Scudda Hay her contract was not renewed that year. She was however re-hired by the studio in 1948 and acted in 'Dangerous Years' that year, again she was uncredited and most of her work didn't make the final draft. Her first credited role was in 'Scudda-Hoo! Scudda-Hay!' also in 1948, her only words were, "Hi Rad!" But yet again most of her work in that film ended up on the cutting room floor.
She next played 'Peggy Martin' in the 1949 film 'Ladies Of The Chorus' before 
getting the role in 'Love Happy' which brought her to the attention of Johnny Hyde.
In the picture on the left of Marilyn with the other girls from the film (Ladies Of The Chorus) Marilyn is on the far left at the end.
Marilyn's notoriety soared when she appeared in the Marx Brothers' Love Happy. The role called for her to walk, in the words of Groucho Marx, "in such a manner as to arouse my elderly libido and cause smoke to issue from my ears." When Marilyn did as directed, she got the job. "And don't do any walking in unpoliced areas," Harpo advised. Love Happy and the publicity tour that followed greatly increased her popularity and image as a screen siren. In 1949 he (Johnny Hyde) of the William Morris Agency, became her mentor and lover. Johnny was a well known agent in Hollywood loved and respected by all in his field.
He first saw Marilyn Monroe in the film Love Happy, and shortly afterwards requested to meet her. The version that I've heard is that John Carroll introduced them at a Palm Springs racquet Club party thrown by Joseph Schenk in January 1949. It was through Johnny that Marilyn was introduced to the major Hollywood studios. 
Johnny Hyde took Marilyn under his wing, he wined, dined, dressed Marilyn. He introduced her to the best and most influential people in Hollywood. Johnny was hopelessly in love with her. He divorced his wife and begged Marilyn to marry him, swearing to leave her millions when he died, which, he dryly promised, would be soon, as he had a serious heart condition. Marilyn loved Johnny but despite his promising to make her rich when he died, she couldn't bring herself to marry for money, for Marilyn it was all about love and although she loved Johnny deeply,
she wasn't 'in love' with him and felt it would hurt him more than if she didn't marry him.
For his part, Johnny made his family promise to take care of Marilyn when he died but they went back on their word and wouldn't even let her see him on his death-bed when he died a year later on the 18th December 1950.
Marilyn was devastated by his death and it is rumoured that she took an overdose of pills at this time, although I have to research that a little more before I can tell you if I think it's true or not.
While she was at Columbia, they had her study with the studio's drama coach, Natasha Lytess. "I said I do anything, whatever she thought would make me an actress!"
Although Natasha Lytess was very unpopular among most of the directors and actors that Marilyn worked with (mainly from her influence over Marilyn) Marilyn relied heavily on her for several years, for both friendship and professional instruction until the two had a falling-out and Marilyn refused to see or speak to her again.