The observatory, funded primarily by the National Science Foundation (NSF) with partial support from NASA, was managed by Cornell University from its completion in 1963 until 2011, after which it was transferred to a partnership led by SRI International.

The telescope's main collecting dish had the shape of a spherical cap 1,000 feet (305 m) in diameter with an 869-foot (265 m) radius of curvature,[9] and was constructed inside a karst sinkhole.

[16] The platform had a rotating, bow-shaped track 93 m (305 ft) long, called the azimuth arm, carrying the receiving antennas and secondary and tertiary reflectors.

[18][19] Among the many Defender projects were several studies based on the concept that a re-entering nuclear warhead would cause unique physical signatures while still in the upper atmosphere.

[18][19] Although the concept appeared to offer a solution to the tracking problem, there was almost no information on either the physics of re-entry or a strong understanding of the normal composition of the upper layers of the ionosphere.

[18][19] On November 6, 1959, Cornell University entered into a contract with ARPA to carry out development studies for a large-scale ionospheric radar probe, exploring how this instrument could also be utilized in radio astronomy and other scientific areas.

Cornell University and Zachary Sears published a request for proposals (RFP) asking for a design to support a feed moving along a spherical surface 133 metres (435 ft) above the stationary reflector.

[27][28][23] George Doundoulakis, who directed research at the General Bronze Corporation in Garden City, New York, along with Zachary Sears, who directed Internal Design at Digital B & E Corporation, New York, received the RFP from Cornell University for the antenna design and studied the idea of suspending the feed with his brother, Helias Doundoulakis, a civil engineer.

George Doundoulakis identified the problem that a tower or tripod would have presented around the center, (the most important area of the reflector), and devised a better design by suspending the feed.

A proposal by the General Bronze Corporation was not selected as it did not meet specifications, according to an editorial response by Donald Cooke (Cornell's spokesperson) to Helias Doundoulakis in a newsletter of the Institute of Electrical and Electronics Engineers (IEEE).

[16][33] Initially, when the maximum expected operating frequency was about 500 MHz, the surface consisted of half-inch galvanized wire mesh laid directly on the support cables.

In 1973, a high-precision surface consisting of 38,000 individually adjustable aluminum panels replaced the old wire mesh,[34] and the highest usable frequency rose to about 5000 MHz.

This allowed installing a suite of receivers, covering the full 1–10 GHz range, that could be easily moved to the focal point, giving Arecibo more flexibility.

[42] An additional US$3 million in bonds were issued by the government of Puerto Rico to fund the Observatory, which were used to modernize power generation and improve other aging infrastructure.

This was used for basic maintenance and for a second, much smaller, antenna to be used for very long baseline interferometry, new Klystron amplifiers for the planetary radar system and student training.

[57] On September 21, 2017, high winds associated with Hurricane Maria caused the 430 MHz line feed to break and fall onto the primary dish, damaging roughly 30 of the 38,000 aluminum panels.

[64][65] On August 10, 2020, an auxiliary platform support cable separated from Tower 4, causing damage to the telescope, including a 100 ft (30 m) gash in the reflector dish.

[16] The firms had developed models of the telescope that showed that the safety factor for Tower 4 had dropped to 1.67, believing that the structure was still safe while repairs could be effected, even if another cable collapsed.

One engineering firm proposed stabilization efforts,[70] while another suggested that they try to sever parts of the instrument platform such as the Gregorian dome to reduce the load.

[16] The third firm made the determination that there was no way to safely repair the damage at this point, as the remaining cables could be suspect, and furthermore that a controlled decommissioning of the telescope was the only effective means to avoid catastrophic failure which would threaten the other buildings on campus.

[71] The NSF took this advice and made the announcement on November 19, 2020 that they would decommission Arecibo over the following few weeks after determining the safest route to do so with a safety exclusion zone immediately put in place.

[73] In the weekend prior to December 1, 2020, wire strands in the receiver's supporting cables had also been snapping apart at a rapid rate, according to Ángel Vázquez, the director of operations.

[77] In late December 2020, Wanda Vázquez Garced, then governor of Puerto Rico signed an executive order for $8 million for the removal of debris and for the design of a new observatory to be built in its place.

"[81] A team from the University of Texas at Austin was able to completely recover and back up the 3 petabytes of data that the telescope had captured since opening in the 1960s by May 2021 before further harm could come to the storage equipment.

[92] The following year, Polish astronomer Aleksander Wolszczan made the discovery of pulsar PSR B1257+12 (Lich), which later led him to discover its three orbiting planets.

[94] In January 2008, detection of prebiotic molecules methanimine and hydrogen cyanide were reported from the observatory's radio spectroscopy measurements of the distant starburst galaxy Arp 220.

[96] In 1974, the Arecibo message, an attempt to communicate with potential extraterrestrial life, was transmitted from the radio telescope toward the globular cluster Messier 13, about 25,000 light-years away.

For these tests, a very wide-band instrumentation recorder captured a large segment of the receiving bandwidth, enabling later verification of other amateur station call signs.

[103] On November 10, 2013, the KP4AO Arecibo Amateur Radio Club conducted a Fifty-Year Commemoration Activation, lasting seven hours on 14.250 MHz SSB, without using the main dish antenna.

[107] In 2014, a video art installation piece titled The Great Silence by artists Jennifer Allora and Guillermo Calzadilla in collaboration with science fiction writer Ted Chiang featured the radio telescope at Arecibo Observatory to represent the search for extraterrestrial life.