As art director at SPI Simonsen supervised the release of over 400 game titles, and had game design or development credit for over twenty games. In addition, he variously held positions of executive art editor and co-editor or executive editor for the SPI magazines Strategy & Tactics, MOVES and Ares. Simonsen was the Charles S. Roberts Awards Hall of Fame inductee for 1977
In 1969 the wargaming hobby fanzine Strategy & Tactics was sold by its founder/publisher Chris Wagner to James F. Dunnigan for $1. Although circulation was only around 1,000 copies, Dunnigan planned on using the magazine to promote new games he was designing. Later he wrote in The Complete Wargames Handbook:
Doing the magazine also brought graphic design ace Redmond Simonsen into SPI. I knew that the magazine, and the games, needed a professional look. Simonsen was a native New Yorker, and a wargamer in addition to being a highly talented artist. So I made him an offer he couldn't refuse: half the business (we later shared some of this with some of the original staff).
The format of Strategy & Tactics (S&T) was ambitiously changed to a bi-monthly magazine with a complete game inside every issue, along with an accompanying historical article. Dunnigan and Simonsen's newly incorporated SPI began publish non-magazine games as well. At that time the main wargame publisher, Avalon Hill, released only one or two new games a year. The response was overwhelming. Simonsen wrote: "Via a program of advertising, S&Ts circulation began to build and sales of SPI games to its readers began to take on serious proportions." Combined with other factors such as a sophisticated computerized customer feedback system the company experienced exponential growth. By the mid-'70s SPI's revenues exceeded $2 million annually, with up to forty employees. Circulation of Strategy and Tactics steadily grew, eventually peaking at over 36,000 by 1980.
Simonsen acted as founding editor for SPI's Ares Magazine, a fantasy/science fiction game magazine following the same approach as Strategy & Tactics, until replaced during the TSR takeover.
Simonsen also wrote fictional backgrounds for various SPI games, notably for StarForce and Battlefleet Mars, often with humorous elements hidden in the text.
It was at SPI that Simonsen coined the term "physical systems design" to describe the application of graphic design concepts to board games. He defined it as follows:
I should perhaps explain what I mean by the term “physical system”. The term is really my personal jargon for the graphic engineering of game elements. The more graphic engineering the artist can build into the game equipment and rules, the easier and more enjoyable becomes the play of the game.
In 1969 however, Simonsen's ability to implement such graphic engineering was limited by SPI's starting capital, which was only "a hundred dollars" borrowed from writer Al Nofi. Accordingly, production standards for their first series of games were comparatively low. While competitor Avalon Hill was owned by the printers Monarch Press, and thus was able to use professional production equipment, SPI was essentially producing game "kits". Designer Greg Costikyan wrote:
SPI's first games had been published with black-and-white maps, printed on paper. The counters for its games were printed on colored paper; buyers had to glue the paper to shirt cardboard, then cut the counters apart with an X-acto knife. Rules were printed on "bedsheets," large sheets of paper folded down to normal letter size, saving the cost of cutting, collating, and binding. And there had been neither box nor counter tray.
Increased revenue and experience led to progressive improvements in production quality, and Simonsen continuously refined the standards for game components. The playing boards ("maps") went from black-and-white to two-color and then full-color. Playing pieces ("counters") became professionally mounted and die-cut, eventually being printed on both sides in full-color. Simonsen now had the means to implement his physical system design concepts. Game designer John Prados recalled that "Redmond prided himself on making at least one graphical innovation each game."
Along with former SPI designer Brad Hessel, he founded Ares Development Corporation to produce computer games. Simonsen had already successfully "ported" the board game Wreck of the B.S.M. Pandora to the Apple II, creating one of the first real-time strategy games. A multi-game contract with Texas Instruments fell through when they pulled out of the home computing business in 1984.
Simonsen then moved to Richardson, Texas where, with Jerry Robinson, he co-founded Microbotics, manufacturers of peripherals for the Amiga platform of home computers. Around 1992 Microbotics closed and he retired from active work, becoming a gaming network moderator for BIX and other places. In 1993 Simonsen contributed to Master of Orion: The Official Strategy Guide (Prima Publishing, 1993), devising a naming-convention for ships. By 1998 he had retired completely and spent his time drawing, writing computer programs and science fiction short stories.
Simonsen had incurred a heart attack in 2004, and suffered two more in early 2005 which led to his hospitalization and death in Garland, Texas on March 10, 2005 at the age of 62.