The Sinclair Executive was the world's first "slimline" pocket calculator, and the first to be produced by Clive Sinclair's company Sinclair Radionics. Introduced in 1972, the calculator was produced in at least two versions with different keyboard markings; a variant called the Sinclair Executive Memory was introduced in 1973.

Its small size was made possible by pulsing current to the Texas Instruments TMS1802 "calculator on a chip" integrated circuit, reducing the power consumption more than tenfold. The Executive was highly successful, making £1.8 million of profit for Sinclair and winning a Design Council Award for Electronics.

The Executive was launched in September 1972 at the price of £79.95 plus VAT, equivalent to £950 in 2025 when adjusted for inflation. This was around half the price of comparable calculators, but still twice the average weekly wage. It was the first pocket calculator, and the first to be mass-produced, and its introduction to the market coincided with a number of other companies entering the calculator market.

The entrepreneur Clive Sinclair, reckoning that the market for "executive toys" was not especially sensitive to price, ordered components for 100,000 calculators. The Executive was highly successful, and made £1.8 million profit for his company Sinclair Radionics. It was well received by both domestic and foreign markets, and US$1.5 million worth of Executives were sold in Japan in early 1974 at six times the price of Japanese models. The parts, consisting of the TMS1802 chip, 22 transistors, 50 resistors and 17 capacitors, cost close to £10, compared with a sale price of almost £80. The Executive impressed the engineers at Texas Instruments, who had used the same chip to produce a longer and wider calculator that was over three times as thick and a great deal more expensive. In 1974, sales of the Executive exceeded £2.5 million, and Sinclair was producing 100,000 calculators each month, of which 55% were exported.

A Sinclair Executive purchased by a Russian diplomat exploded in his breast pocket, allegedly leading to an official Soviet investigation. It was found that it had been left on by accident, leading to a drain on the batteries that overheated them until they burst.

The calculator was significantly smaller than any of its competitors, and the first that could easily be carried in a pocket. According to a Sinclair executive quoted in the Financial Times, "one must always bear a packet of cigarettes in mind as the ideal size", possibly a quip on Clive Sinclair's smoking habit. The Executive weighed 2.5 ounces (71 g) and measured 56 by 138 by 9 millimetres (2.20 in × 5.43 in × 0.35 in). The case, designed by Iain Sinclair, was made of black injection-moulded polycarbonate and required flexible glue to hold the two halves together.

Design Magazine described it as "at once a conversation piece, a rich man's plaything and a functional business machine". One example is on display at the Museum of Modern Art in New York City, and the futuristic design earned it the Design Council Award for Electronics in 1973. It was the first calculator designed for aesthetic appeal, and New Scientist described it as "not so much a professional calculator – more a piece of personal jewellery".

As well as four-function arithmetic, the Executive could compute squares, reciprocals, and multiply or divide by a fixed constant. The Executive could display results to two, four, or six decimal places, or use a floating decimal point.