Syed Omar Bin Ali Aljunied made a lot of contributions to Singapore. He came from a family of wealthy and prominent merchants called the Aljunieds.

The Aljunieds along with the Alkaffs and Alsagoffs were the three most outstanding and wealthy Arab families in Singapore for a short period of time. The Aljunied family contributed large sums of money to buildings such as the Aljunied Islamic School (Madrasah Aljunied Al-Islamiah), which was built in 1927. The Aljunieds also contributed large amounts of money for the building of the Town Hall.

One of Syed Omar's biggest contribution to Singapore was his giving away of the land and the Masjid Kampong Melaka (Masjid Omar Kampong Melaka or Malacca Mosque) in Chinatown which was the first place of worship constructed in Singapore. In 1981 to 1982, after almost a hundred years of use, the original structure of a temporary timber building, was demolished and reconstructed into a brick mosque that had a tall minaret with a small roof dome which was added at the entrance of the mosque. This reconstruction coincided with the laying of a new road through Kampong Malacca which brought worshippers from the surrounding area. Today, the mosque is in much the same state as it was after the last reconstruction — a simple building that is well complemented by its surrounding space. With a sitting capacity of about 1,000 people, it is the focal point for office workers during daily and Friday prayers.
He also gave away the land for the St Andrew's Cathedral and the land for Dr Tan Tock Seng paupers' hospital which later became Tan Tock Seng Hospital and was resited to Moulmein Road.

Syed Omar furthermore donated a large burial ground at Jalan Kubor (near Victoria Street) and built another mosque in Bencoolen Street. Large wells with granite sides were also dug behind Fort Canning, Selegie Road, Pungulu Kisang and Telok Ayer with the rest of the Aljunieds to supply water to the early residents of Singapore.

One of Syed Omar's earliest contributions was the building of four community wells at his own expense and the donation of land for the Bukit Wakaff Cementery at Grange Road. Mr. Syed Ali was also a philanthropist. He is best known for filling in a swamp purchased by his father, Mr. Syed Mohammed, who was also Mr. Syed Omar’s uncle-land that would become Weld Road and Jalan Besar. Three bridges in the area were also built at his expense.